Add Product Intelligence estimation weight policy

What does this MR do and why?

Related to https://gitlab.com/gitlab-org/product-intelligence/-/issues/586.

This adds a policy for ~"group::product intelligence" to add a comment reminding team members weekly to estimate and put a weight on open issues for the current milestone.

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review