Add Maintainer Retainer Program (MRP) documentation draft

[danbaruka]

Page or section

docs/maintainer-retainer/ (new documentation section in devex)

Issue description

There is currently no centralized documentation in dev-ex explaining the Maintainer Retainer Program (MRP), its purpose, or the distinction between Core Maintainers and Community Maintainers.

Intersect OSO requested a reusable documentation draft to be reviewed in dev-ex before extending similar content to MRP-supported project repositories.

Proposed change

Add a new documentation file under a dedicated docs folder (e.g. docs/maintainer-retainer/maintainer-retainer.md) that includes:

• A brief overview of the Maintainer Retainer Program
• Definition of Core Maintainers
• Definition of Community Maintainers
• A link to the official OSC / Intersect MRP page as the source of truth
• Guidance that individual maintainer names should be managed externally (via OSC) to avoid stale repository documentation

Reference link:
https://committees.docs.intersectmbo.org/intersect-open-source-committee/about/paid-open-source-model-posm/maintainer-retainer/project-list

Checks

• I searched existing issues and discussions
• This is about documentation (not a feature request or bug)