Draft: POC for stage needs

What does this MR do and why?

This is a proof of concept for implementing a needs that references stages instead of builds.

Related #220758

FF Rollout issue #344662

How to set up and validate locally

1. Create a project with the following pipeline config

stages:
  - first
  - second

sample_job:
  stage: first
  script:
    - echo 1

second_sample_job:
  stage: first
  script:
    - echo 1

test_job:
  needs:
    - name: first
      type: stage

2. Verify that the test_job requires the stage called first to exist
3. TODO: Verify that the test_job waits for all jobs in the first stage to complete before running.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.