Add configurable deployment exclude list to allow deploying .github content

[Copilot]

The action currently hardcodes deployment excludes, which prevents deploying .github from build output. This change makes deployment excludes configurable while preserving current safety defaults when no override is provided.

• New input: configurable deploy excludes

  • Added a new optional exclude input (multiline) in action.yml.
  • Parsed into ActionInterface.exclude in src/constants.ts.

• Deploy behavior update

  • Reworked rsync exclude construction in src/git.ts:
    • If exclude is provided, use that list.
    • If not provided, keep existing defaults (.ssh, .git, .github).
    • Continue excluding the temporary deployment directory when deploying from workspace root.

• Documentation updates

  • Added exclude to the README configuration table.
  • Added an explicit warning that providing exclude replaces default excludes.

• Targeted test coverage

  • Added tests in __tests__/git.test.ts for:
    • default exclude fallback behavior
    • custom exclude override behavior

Example workflow usage:

- name: Deploy 🚀
  uses: JamesIves/github-pages-deploy-action@v4
  with:
    folder: dist
    exclude: |
      .github
      file.xml