Notification Triggers are now a type string

[sebasslash]

Description

This PR converts the Triggers field in Create/UpdateNotificationConfigurationOpts from []string to []NotificationTriggerType. I've also added a validation function to ensure any value passed in the array is a valid NotificationTriggerType... the go compiler doesn't enforce it at compile time (See #341).

The Triggers field for NotificationConfiguration will remain of type []string. This is due to the inability of the jsonapi package to unmarshal strings into an array of typed strings. Performing some type casting after unmarshalling is an effort that was not deemed to be worthwhile since this is a specific use case.

Testing plan

To run integration tests:

go test -run TestNotificationConfiguration -v ./... -tags=integration

Output from tests (HashiCorp employees only)

=== RUN   TestNotificationConfigurationList
=== RUN   TestNotificationConfigurationList/with_a_valid_workspace
    notification_configuration_integration_test.go:36: paging not supported yet in API
=== RUN   TestNotificationConfigurationList/with_list_options
    notification_configuration_integration_test.go:42: paging not supported yet in API
=== RUN   TestNotificationConfigurationList/without_a_valid_workspace
--- PASS: TestNotificationConfigurationList (2.58s)
    --- SKIP: TestNotificationConfigurationList/with_a_valid_workspace (0.17s)
    --- SKIP: TestNotificationConfigurationList/with_list_options (0.00s)
    --- PASS: TestNotificationConfigurationList/without_a_valid_workspace (0.00s)
=== RUN   TestNotificationConfigurationCreate
=== RUN   TestNotificationConfigurationCreate/with_all_required_values
=== RUN   TestNotificationConfigurationCreate/without_a_required_value
=== RUN   TestNotificationConfigurationCreate/without_a_required_value_URL_when_destination_type_is_generic
=== RUN   TestNotificationConfigurationCreate/without_a_valid_workspace
=== RUN   TestNotificationConfigurationCreate/with_an_invalid_notification_trigger
=== RUN   TestNotificationConfigurationCreate/with_email_users_when_destination_type_is_email
=== RUN   TestNotificationConfigurationCreate/without_email_users_when_destination_type_is_email
--- PASS: TestNotificationConfigurationCreate (2.35s)
    --- PASS: TestNotificationConfigurationCreate/with_all_required_values (0.20s)
    --- PASS: TestNotificationConfigurationCreate/without_a_required_value (0.00s)
    --- PASS: TestNotificationConfigurationCreate/without_a_required_value_URL_when_destination_type_is_generic (0.00s)
    --- PASS: TestNotificationConfigurationCreate/without_a_valid_workspace (0.00s)
    --- PASS: TestNotificationConfigurationCreate/with_an_invalid_notification_trigger (0.00s)
    --- PASS: TestNotificationConfigurationCreate/with_email_users_when_destination_type_is_email (0.18s)
    --- PASS: TestNotificationConfigurationCreate/without_email_users_when_destination_type_is_email (0.15s)
=== RUN   TestNotificationConfigurationRead
=== RUN   TestNotificationConfigurationRead/with_a_valid_ID
=== RUN   TestNotificationConfigurationRead/when_the_notification_configuration_does_not_exist
=== RUN   TestNotificationConfigurationRead/when_the_notification_configuration_ID_is_invalid
--- PASS: TestNotificationConfigurationRead (1.84s)
    --- PASS: TestNotificationConfigurationRead/with_a_valid_ID (0.14s)
    --- PASS: TestNotificationConfigurationRead/when_the_notification_configuration_does_not_exist (0.12s)
    --- PASS: TestNotificationConfigurationRead/when_the_notification_configuration_ID_is_invalid (0.00s)
=== RUN   TestNotificationConfigurationUpdate
=== RUN   TestNotificationConfigurationUpdate/with_options
=== RUN   TestNotificationConfigurationUpdate/with_invalid_notification_trigger
=== RUN   TestNotificationConfigurationUpdate/with_email_users_when_destination_type_is_email
=== RUN   TestNotificationConfigurationUpdate/without_email_users_when_destination_type_is_email
=== RUN   TestNotificationConfigurationUpdate/without_options
=== RUN   TestNotificationConfigurationUpdate/when_the_notification_configuration_does_not_exist
=== RUN   TestNotificationConfigurationUpdate/when_the_notification_configuration_ID_is_invalid
--- PASS: TestNotificationConfigurationUpdate (3.43s)
    --- PASS: TestNotificationConfigurationUpdate/with_options (0.31s)
    --- PASS: TestNotificationConfigurationUpdate/with_invalid_notification_trigger (0.00s)
    --- PASS: TestNotificationConfigurationUpdate/with_email_users_when_destination_type_is_email (0.20s)
    --- PASS: TestNotificationConfigurationUpdate/without_email_users_when_destination_type_is_email (0.15s)
    --- PASS: TestNotificationConfigurationUpdate/without_options (0.19s)
    --- PASS: TestNotificationConfigurationUpdate/when_the_notification_configuration_does_not_exist (0.12s)
    --- PASS: TestNotificationConfigurationUpdate/when_the_notification_configuration_ID_is_invalid (0.00s)
=== RUN   TestNotificationConfigurationDelete
=== RUN   TestNotificationConfigurationDelete/with_a_valid_ID
=== RUN   TestNotificationConfigurationDelete/when_the_notification_configuration_does_not_exist
=== RUN   TestNotificationConfigurationDelete/when_the_notification_configuration_ID_is_invalid
--- PASS: TestNotificationConfigurationDelete (1.79s)
    --- PASS: TestNotificationConfigurationDelete/with_a_valid_ID (0.26s)
    --- PASS: TestNotificationConfigurationDelete/when_the_notification_configuration_does_not_exist (0.12s)
    --- PASS: TestNotificationConfigurationDelete/when_the_notification_configuration_ID_is_invalid (0.00s)
=== RUN   TestNotificationConfigurationVerify
=== RUN   TestNotificationConfigurationVerify/with_a_valid_ID
=== RUN   TestNotificationConfigurationVerify/when_the_notification_configuration_does_not_exists
=== RUN   TestNotificationConfigurationVerify/when_the_notification_configuration_ID_is_invalid
--- PASS: TestNotificationConfigurationVerify (1.84s)
    --- PASS: TestNotificationConfigurationVerify/with_a_valid_ID (0.19s)
    --- PASS: TestNotificationConfigurationVerify/when_the_notification_configuration_does_not_exists (0.11s)
    --- PASS: TestNotificationConfigurationVerify/when_the_notification_configuration_ID_is_invalid (0.00s)
PASS
ok      github.com/hashicorp/go-tfe     14.622s
?       github.com/hashicorp/go-tfe/examples/organizations      [no test files]
?       github.com/hashicorp/go-tfe/examples/workspaces [no test files]
?       github.com/hashicorp/go-tfe/mocks       [no test files]

[barrettclark]

This all looks reasonable to me