Establish guidelines for CI/CD template submissions from Technology Partners

Proposal

Based on this MR: !51415 (closed) and later discussions in Slack, it seems we'll have a new "class" of CI/CD templates: CI/CD templates submitted by GitLab Technology Partners: https://about.gitlab.com/partners/technology-partners/

I believe we need to establish guidelines for every step of this process. Including:

1. Guidelines for creating the template itself, with standards that can be used across all templates. This includes:
   1. Where to put the template, and naming standards?
   2. What syntax is recommended, and what syntax to avoid?
   3. Required style?
   4. Required comments? For example, explain if it's intended to be added with include or used standalone. Explanation of variables, prerequisites, etc.
2. MR review process:
   1. Who to ping first?
   2. How to demonstrate the template in action?
3. Template maintenance:
   1. Who is responsible for maintenance?
   2. How is the template maintained? If there are issues, who should the public contact, and how should they do it?
   3. What happens to the template if the partnership expires?

Current Documentation

The current template guide is generally for internal use: https://docs.gitlab.com/ee/development/cicd/templates.html

@DarwinJS wrote some details at https://gitlab.com/guided-explorations/ci-cd-plugin-extensions/design-guide-and-templates-for-ci-cd-extensions, but I don't see this as clear/precise enough for the authors/reviewers.