feat: support merging jobs for tfmigrate and terraform

[suzuki-shunsuke]

Close #223

Added new actions plan and apply.
You can replace actions terraform-plan and tfmigrate-plan with plan, and can replace terraform-apply and tfmigrate-apply with apply.
You can merge jobs for tfmigrate with jobs for terraform.
You can simplify workflows.

This pull request keeps the compatibility.

How to merge jobs

1. Fix outputs of setup job
2. Remove jobs for tfmigrate
3. (Optional) Rename jobs terraform-plan and terraform-apply to plan and apply
4. Fix TFACTION_JOB_TYPE
5. Replace actions terraform-plan and terraform-apply with plan and apply

1. Fix outputs of setup job

Before

    outputs:
      tfmigrate_targets: ${{ steps.list-targets.outputs.tfmigrate_targets }}
      terraform_targets: ${{ steps.list-targets.outputs.terraform_targets }}

      matrix:
        target: ${{fromJSON(needs.setup.outputs.terraform_targets)}}

After

    outputs:
      targets: ${{ steps.list-targets.outputs.targets }}

      matrix:
        target: ${{fromJSON(needs.setup.outputs.targets)}}

4. Fix TFACTION_JOB_TYPE

Before

TFACTION_JOB_TYPE: terraform

After

TFACTION_JOB_TYPE: ${{matrix.target.job_type}}

5. Replace actions terraform-plan and terraform-apply with plan and apply

You don't need to change inputs.

Before

     - uses: suzuki-shunsuke/tfaction/terraform-plan@v0.7.3

     - uses: suzuki-shunsuke/tfaction/terraform-apply@v0.7.3

After

     - uses: suzuki-shunsuke/tfaction/plan@v0.7.4

     - uses: suzuki-shunsuke/tfaction/apply@v0.7.4