Add a CODEOWNERS file and set up review assignment automation for Rules Management Team

[nikitaindik]

Description

@elastic/security-detection-rule-management team would like to review documentation changes for features that are owned by the team.

TODO:

• Add a CODEOWNERS file and specify relevant paths relevant for the Rules Management
• Set up GitHub automation to auto-assign a reviewer from the Rules Management team to every related docs PR

Related links / assets

No response

Which documentation set needs improvement?

Unknown / Not applicable

Software version

Not applicable

Collaborators

Not applicable

Timeline / deliverables

Not applicable