v6.0.0

Add skip-plandiff option and fix workspace variable usage @jamengual (#89)

This pull request adds support for skipping plan diff validation in the `action.yml` workflow, allowing users to bypass plan preparation and diff validation steps if desired. It also refactors how plan files are selected and referenced throughout the workflow, and standardizes the use of `${GITHUB_WORKSPACE}` for file paths. These changes improve flexibility and maintainability of the workflow.

Plan Diff Skipping and Conditional Logic

• Added a new input skip-plandiff to action.yml to allow skipping plan diff validation, with corresponding conditional logic throughout the workflow to support this behavior. [1] [2]
• Introduced a new step Determine Plan File to select the appropriate plan file and filename based on whether plan diff is skipped or not, and updated downstream steps to use this output. [1] [2] [3]

File Path Standardization

• Replaced usages of ${{ github.workspace }} with ${GITHUB_WORKSPACE} for all file output and manipulation operations, ensuring consistency and reliability in file path references. [1] [2] [3] [4] [5]

Workflow Improvements

• Updated conditional logic for Infracost-related steps and Terraform apply to account for the new skip-plandiff input, ensuring correct execution flow when plan diff is skipped. [1] [2]
• Added logic to conditionally set the --skip-init flag for Terraform apply, depending on whether plan diff was run.

Minor Enhancements

• Added a conditional to the Atmos installation step so it only runs when a version is specified.