Add possibility to add custom command

[MathieuSoysal]

Introduction

Currently, the GitHub Action uses a library injection to add JavaDoc inside the pom.

Problem

With this solution, we can't config the GitHub Actions to use the custom JavaDoc library inside the current project.
And we can't add arguments for the JavaDoc generation.

Solution

We can add a custom command like this:

      - name: Deploy JavaDoc 🚀
        uses: MathieuSoysal/Javadoc-publisher.yml@v2.0.4
        with:
          custom-command: mvn javadoc:aggregate pl name

The resources to help the implementation:

• https://docs.github.com/en/actions/learn-github-actions/expressions
• https://docs.github.com/en/actions/using-jobs/using-conditions-to-control-job-execution
• https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions