Add install-svn composite action

[slawekjaranowski]

As composite actions are external to workflow - I need it add as separate commit.

Next we cen use this one action in workflow instead of repeat the same steps multiple time.

[slawekjaranowski]

tested in

• Install subversion on all operating systems #213

[hboutemy]

FTR https://docs.github.com/en/actions/tutorials/create-actions/create-a-composite-action
and https://medium.com/@reach2shristi.81/reusable-workflows-and-composite-actions-in-github-actions-013b177e8b6c

oh, I did not get the new directory for composite action .github/actions/install-svn/action.yml and normalized action.yml file name
that will be referenced in workflows (once merged to v4 branch) as

jobs:
  run-tests:
    runs-on: ubuntu-latest
    steps:
      - name: Install Subversion
        uses: apache/maven-gh-actions-shared/.github/actions/install-svn@v4

great learning, thanks

[hboutemy]

found the reference doc for composite action (vs javascript or docker ones)
https://docs.github.com/en/actions/reference/workflows-and-actions/metadata-syntax#runs-for-composite-actions