Add workspace run task stage property

[glennsarti]

Description

This commit adds the stage attribute to the Workspace Run Task
Resource and Data Source. Note that this is in beta for the
Resource. This commit adds acceptance tests, and optionally
test the Beta features.

This commit also adds descriptions for the Workspace Run Task
attributes.

Testing plan

1. Acceptance tests cover the testing plan. Beta features require a feature flag to be enabled on TFC.

External links

Include any links here that might be helpful for people reviewing your PR. If there are none, feel free to delete this section.

• go-tfe documentation
• API documentation

Output from acceptance tests

With beta tests enabled

?       github.com/hashicorp/terraform-provider-tfe     [no test files]
=== RUN   TestAccTFEWorkspaceRunTask_create
--- PASS: TestAccTFEWorkspaceRunTask_create (38.84s)
=== RUN   TestAccTFEWorkspaceRunTask_beta_create
--- PASS: TestAccTFEWorkspaceRunTask_beta_create (34.31s)
=== RUN   TestAccTFEWorkspaceRunTask_import
--- PASS: TestAccTFEWorkspaceRunTask_import (27.11s)
PASS
ok      github.com/hashicorp/terraform-provider-tfe/tfe 100.750s
?       github.com/hashicorp/terraform-provider-tfe/version     [no test files]

[cam-stitt]

Seems good to me. Would like someone from the CLI team to cover this also.

[glennsarti]

Rebased due to changelog merge conflict

[brandonc]

This looks great. The only problem is that we released 0.36.0 and now the CHANGELOG needs to be moved to a new ## Unreleased section.

I also would hesitate to merge this unless it was available to customers. Can it wait until GA or is there some reason to publish this early?

[glennsarti]

I also would hesitate to merge this unless it was available to customers.

It is available in TFC for everyone, but are you worried about TFE?

[glennsarti]

Fixed the changelog

[brandonc]

@glennsarti nope- I didn't realize the flag had been enabled for customers.