Implement needs[].parallel.matrix

[firecow]

https://gitlab.com/gitlab-org/gitlab/-/issues/254821 Is in release candidate. This is looking like, what gitlab.com wants to implement.

test:
  needs:
    - job: build
      parallel:
        matrix:
          - PLATFORM: ubuntu
            STACK: [ruby, python]

# depends on build[ubuntu, ruby] and build[ubuntu, python]

test:
  needs:
    - job: build
      parallel:
        matrix:
          - PLATFORM: ubuntu

# depends on build[ubuntu, *]

test:
  needs:
    - job: build
      parallel:
        matrix:
          - PLATFORM: ubuntu
            STACK: []

# depends on build[ubuntu]