Add runner registration related properties to OpenShift Operator

What does this MR do?

Adds runner registration related properties to the OpenShift Operator documentation.

Since this are new properties added in the Operator yet to be released, it still states tbd as Operator version. This will be updated, once the code change MR is merged and released. Until then, this MR stays in draft status.

Related issues

Docs for gitlab-org/gl-openshift/gitlab-runner-operator!105 (merged)

Refs: gitlab-org/gl-openshift/gitlab-runner-operator#96 (closed)

Author's checklist

• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• Request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.
• Update table with released Operator version

Review 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 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.
  • 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 above reviews. Maintainer's review can occur before or after a technical writer review.
• Ensure a release milestone is set.