Update custom tag reference in CI schema

What does this MR do and why?

Fix for #348666 (comment 1106425782)

Adds support for the custom yaml keyword !reference for the keywords image, tags, and script.

This also removes the title from the CI schema so the annotations don't render it for every keyword.

Screenshots or screen recordings

For the title removal:

Before	After

How to set up and validate locally

1. Go to the Pipeline Editor (CI/CD > Editor)
2. Copy-paste the following into your .gitlab-ci.yml file:

   .base:
     image: busybox
     tags: gitlab-org
     stage: test
   
   job:
     image: !reference [.base, image]
     tags:
       - !reference [.base, tags]
     stage: !reference [.base, stage]
     script: echo

3. Verify that no linting errors show up.

MR acceptance checklist

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