Support multi-line arguments

[bigdaz]

Supplying the entire argument list on a single line can be cumbersome and make the workflow file difficult to read. A relatively simple solution would be to allow arguments to be supplied as a multi-line input. So instead of:

 - name: Build
      uses: gradle/gradle-build-action@v2
      with:
        arguments: build --info -PsomeService.prod.apiKey=${{ secrets.SOME_SERVICE_API_KEY }} -PsomeService.prod.secret=${{ secrets.SOME_SERVICE_API_SECRET }} -PsomeService.prod.projectId=${{ secrets.SOME_SERVICE_PROJECT_ID }}

one could use:

- name: Build
      uses: gradle/gradle-build-action@v2
      with:
        arguments: |
             build --info 
             -PsomeService.prod.apiKey=${{ secrets.SOME_SERVICE_API_KEY }} 
             -PsomeService.prod.secret=${{ secrets.SOME_SERVICE_API_SECRET }} 
             -PsomeService.prod.projectId=${{ secrets.SOME_SERVICE_PROJECT_ID }}

I think this option is preferable to a structured input parameter for properties since it keeps the action API simpler and is likely easier for new users to learn and understand.

Thanks @vlsi for the inspiration: #18 (comment).

[vlsi]

By the way, https://github.com/burrunan/gradle-cache-action#usage supports multiline arguments and properties

[bigdaz]

Turns out this was already working, and just needed a test and docs :).