Add new syntax of workflow:auto_cancel:on_new_commit

What does this MR do and why?

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This is the second step of #412473 (closed).

1. Add auto_cancel_on_new_commit to ci_pipeline_me... (!137520 - merged)
2. <--HERE-->
3. Add `interruptible` to trigger jobs (!138508 - merged)
4. Add auto_cancel:on_new_commit to canceling redu... (!139358 - merged)
5. workflow:rules:auto_cancel (#436467 - closed)

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This MR adds a new syntax of workflow:auto_cancel:on_new_commit.

This new syntax will allow users to define the auto-cancel behavior of pipelines when a new commit is pushed to the same branch.

These missing parts will be added later;

• CI Schema file for the new syntax
• Documentation of the new syntax

Screenshots or screen recordings

workflow:
  auto_cancel:
    on_new_commit: conservative # (default), other options: "interruptible", "disabled"

MR acceptance checklist

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