Adding container args as well as improving docs

[gvegayon]

This pull request includes several updates to the twostep-container-build GitHub Action, focusing on enhancing its functionality and documentation. The changes include modifications to workflow files, updates to the README, and improvements to the action's configuration and examples.

Workflow Updates:

• Renamed the test job to test-no-args and added a new job test-with-args in .github/workflows/test-twostep-container-build.yml to test the action with arguments. [1] [2]

Documentation Updates:

• Updated the README.md to include new sections on inputs and outputs, and modified the example usage to reflect the latest changes. [1] [2] [3] [4] [5]

Action Configuration Updates:

• Enhanced the twostep-container-build/action.yml with additional inputs for build arguments and defined outputs for the action. [1] [2] [3] [4]

Example Updates:

• Updated examples/Containerfile and examples/Containerfile.dependencies to reflect the new build process and added labels for better tracking. [1] [2]
• Added a Makefile in the examples directory to simplify the build process for users.

[gvegayon]

Hey @damonbayer, this is ready for review. It took me longer than I wanted b/c of the way that ARG works... it is cleared after the FROM statement. I think you knew that, but I didn't! The way in which the action is now should do what you want.

[damonbayer]

@gvegayon Thanks for this! I think I'm too much of a novice to provide a good review. The first time I ever edited a containerfile was last week. That said, the examples look good.