Documents roulette experiment for GitLab chart

Why is this change being made?

Updates the Distribution workflow to communicate that the gitlab-org/charts repo will be doing an experiment with the reviewer roulette, as per:

• gitlab-org/charts/gitlab!3252 (diffs)
• gitlab-org/distribution/team-tasks#1304 (closed)

Blocking

The roulette MR should be merged right after this one.

gitlab-org/charts/gitlab!3252 (merged)

Second Attempt

gitlab-org/charts/gitlab!3319 (merged)

Announcement

To be pasted on whats-happening-at-gitlab. Replace the links properly on slack:

The Distribution will be experimenting using the GitLab Reviewer Roulette on the `gitlab-org/charts` project.

**For authors**: 
- If you see the reviewer roulette in your MR, please prioritize the suggestion when assigning the first reviewer, and keep using the `wokflow::ready for review` label.
- You can assign a reviewer and apply the label with only one command: `@gitlab-bot ready @username-of-someone`. 

**For reviewers**:
- If you've set yourself as a reviewer of this project in your GitLab team yaml file, you should expect getting review requests from authors of this project.
- While it's expected that you do the review, it's not mandatory. You should always acknowledge when you're at capacity, and be honest with the author if you'll not be able to start the review within the expected [SLO](https://about.gitlab.com/handbook/engineering/development/enablement/systems/distribution/merge_requests.html#service-level-objective). If that's the case, please set your status to busy so that the roulette won't suggest you again for other MRs.
- If your team yaml file is outdated and you actually are not a reviewer of this project anymore, and don't want to be considered as a reviewer by the roulette, you can remove this project from your team yaml file so that the roulette will stop considering you as a reviewer.
- If you want to know more about the reviewer roulette and how you can control your availability so that you don't get overloaded with review requests, please read: https://docs.gitlab.com/ee/development/code_review.html#reviewer-roulette.
- The process for Distribution maintainers is not expected to change.

For more information about this change have a look at:

- https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/126266
- https://gitlab.com/gitlab-org/distribution/team-tasks/-/issues/1304
- https://gitlab.com/gitlab-org/charts/gitlab/-/merge_requests/3319

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added, and the content is SAFE
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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