Implement ssh-key and ssh-known-hosts support for GHA

[mathias-luedtke]

test_ici:
    runs-on: ubuntu-latest
    steps:
      - uses: 'mathias-luedtke/industrial_ci@feature/github-ssh-key'
        with:
          ssh-key: ${{ secrets.private_key }}
        env:
          ROS_DISTRO: "humble"
          TARGET_WORKSPACE: "git+ssh://git@github.com/mathias-luedtke/testpriv.git#main"

[AndyZe]

Doesn't seem to work for me yet

Error: Unable to resolve action `myorg/myrepo1`, repository not found. Unable to resolve action `myorg/myrepo2`, repository not found. Unable to resolve action `myorg/myrepo3`, repository not found....

Here's my industrial_ci.yml in case I made a mistake there:

jobs:
  industrial_ci:
    strategy:
      matrix:
        env:
          - {ROS_DISTRO: humble, ROS_REPO: main}
    env:
      CCACHE_DIR: "${{ github.workspace }}/.ccache" # Enable ccache
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4 # clone target repository
      - uses: 'myorg/myrepo1@main'
        with:
          ssh-key: ${{ secrets.REPO1 }}
      - uses: 'myorg/myrepo2@main'
        with:
          ssh-key: ${{ secrets.REPO2 }}
      - uses: 'myorg/myrepo3@ros2'
        with:
          ssh-key: ${{ secrets.REPO3 }}
...
      - uses: actions/cache@v4 # fetch/store the directory used by ccache before/after the ci run
        with:
          path: ${{ env.CCACHE_DIR }}
          # This configuration will always create a new ccache cache starting off from the previous one (if any).
          # In this simple version it will be shared between all builds of the same ROS_REPO and ROS_REPO
          # and might need some fine-tuning to match the use case
          key: ccache-${{ matrix.ROS_DISTRO }}-${{ matrix.ROS_REPO }}-${{github.run_id}}
          restore-keys: |
            ccache-${{ matrix.ROS_DISTRO }}-${{ matrix.ROS_REPO }}-
      - uses: 'mathias-luedtke/industrial_ci@feature/github-ssh-key'
        env: ${{matrix.env}}

[mathias-luedtke]

@AndyZe: My example only works for single deploy key and ideally with a *.repos file.
If you need multiple deploy keys, you could use https://github.com/webfactory/ssh-agent, like in https://github.com/mathias-luedtke/sshtest/blob/main/.github/workflows/main.yml#L40

[AndyZe]

Alright, well I'm going to stick with what I documented in #900 then. It works well, not too difficult.