feat: add workspaces to Tekton pipeline for git repo creds and registry creds

[HarikrishnanBalagopal]

Also put relative paths in the Tekton pipeline when there is no git repo. This makes the pipeline more usable.

Example:

    - name: build-push-1
      params:
        - name: IMAGE
          value: $(params.image-registry-url)/golang
        - name: DOCKERFILE
          value: '<TODO: fill this prefix starting from the root of the git repo>/golang/Dockerfile'
        - name: CONTEXT
          value: '<TODO: fill this prefix starting from the root of the git repo>/golang'

[github-actions]

Thanks for making a pull request! 😃
One of the maintainers will review and advise on the next steps.