[Bugfix] Fixes #417 - Force terraform command to apply if a plan file is being used

[duckpuppy]

If a plan file is being used in the TerraformApplyCommand, then the only
applicable Terraform subcommand is apply. This PR forces apply to be used if
a plan file is set. This works whether the plan file was created with or without
the -destroy argument.

• Force the use of terraform apply in TerraformApplyCommand if a planFile is present
• Update changelog

Merge Checklist

• Have you linked this Pull Request to an Issue?
• Have you updated any relevant README files, to explain how this new feature works (with examples)?
• Have you added relevant test cases for your change?
• Do all tests and code style checks pass with ./gradlew check --info?
• Have you successfully run your change in a pipeline in a Jenkins instance?
• Have you updated the CHANGELOG?

[kmanning]