Simplify job control page by creating dedicated rules page

What does this MR do?

This is part 2, following Start copy editing job control page (!147771 - merged).

In this MR, we split the job control page into two. One page is dedicated to using the rules keyword in jobs to control when they are added to pipelines, while the rest of the content about controlling jobs with other keywords stays on the original page.

As part of this, I also improved the content that got moved over to the new page, including:

• Rearranging the content on the new page into better groupings/nesting.
• Simplifying and clarifying the language.
• Improving headers
• Removing headers for small sections that could be combined together.
• Removing outdated or deprecated (only/except) content.
• Removing duplicate content that was already on this page, or other pages.

As usual in this kind of MR, links to the moved content also had to be updated.

Review app pages:

• https://main-ee-149491.docs.gitlab-review.app/ee/ci/jobs/job_rules.html
• https://main-ee-149491.docs.gitlab-review.app/ee/ci/jobs/job_control.html

Screenshots

Before	After
	job_control.md: job_rules.md:

Related issues

• Related to !147771 (merged)
• Related to https://gitlab.com/gitlab-org/technical-writing/-/issues/981

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding a new page, add the product tier badge under the H1 topic title.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.