Add a atmos terraform apply-last-plan command

[Gowiem]

Describe the Feature

Add a new terraform subcommand: apply-last-plan that will pick up the written *.planfile for the given component + stack and will execute terraform apply <planfile name>.planfile <extra args>.

Use Case

A really common workflow that I followed when working with vanilla terraform was the following:

1. Run terraform plan -out run.plan
2. Check and confirm the plan
3. terraform apply run.plan

With atmos, this doesn't work. When you run a plan, it outputs a planfile, but when passing that planfile as an extra argument to apply, it causes the following error:

Executing command:
/usr/bin/terraform apply -var-file dev-ssm-parameters.terraform.tfvars.json dev-ssm-parameters.planfile

│ Error: Can't set variables when applying a saved plan
│
│ The -var and -var-file options cannot be used when applying a saved plan file, because a saved plan includes the variable values that were set when it was created.

exit status 1

That is due to the -var-file arg atmos passes obviously, which we would not pass if we implemented the apply-last-plan subcommand. It also has the added benefit that the atmos user doesn't need to specify the planfile name in the command, which is duplicate information anyway.

Alternatives Considered

N/A

Additional Context

I'll have someone from my team or myself work on this if there is interest to implement!

[aknysh]

@Gowiem we have the flag already --from-plan

Run

atmos terraform --help

'atmos terraform apply' and 'atmos terraform deploy' commands support '--from-plan' flag. If the flag is specified, the commands will use the previously generated 'planfile' instead of generating a new 'varfile'

'atmos' supports all native 'terraform' commands.
In addition, 'component' and 'stack' are required in order to generate variables for the component in the stack.
atmos terraform <command> <component> -s <stack> [options]
atmos terraform <command> <component> --stack <stack> [options]

Additions and differences from native terraform:
 - before executing other 'terraform' commands, 'atmos' calls 'terraform init'
 - 'atmos terraform deploy' command executes 'terraform plan' and then 'terraform apply'
 - 'atmos terraform deploy' command supports '--deploy-run-init=true/false' flag to enable/disable running 'terraform init' before executing the command
 - 'atmos terraform deploy' command sets '-auto-approve' flag before running 'terraform apply'
 - 'atmos terraform apply' and 'atmos terraform deploy' commands support '--from-plan' flag. If the flag is specified, the commands will use the previously generated 'planfile' instead of generating a new 'varfile'
 - 'atmos terraform clean' command deletes the '.terraform' folder, '.terraform.lock.hcl' lock file, and the previously generated 'planfile' and 'varfile' for the specified component and stack
 - 'atmos terraform workspace' command first calls 'terraform init -reconfigure', then 'terraform workspace select', and if the workspace was not created before, it then calls 'terraform workspace new'
 - 'atmos terraform import' command searches for 'region' in the variables for the specified component and stack, and if it finds it, sets 'AWS_REGION=<region>' ENV var before executing the command
 - 'atmos terraform generate backend' command generates the backend file for the component in the stack
 - 'atmos terraform generate varfile' command generates a varfile for the component in the stack
 - 'atmos terraform shell' command configures an environment for the component in the stack and starts a new shell allowing executing all native terraform commands

[aknysh]

Please add your new --skip-init flag from the other PR to the help "Additions and differences from native terraform:", right after "- before executing other 'terraform' commands, 'atmos' calls 'terraform init'"

[Gowiem]

@aknysh ah damn -- I missed --from-plan. Great to know about, thanks for the heads up! I'll close this out.

And re: #193 -- Will do!