Improve guidelines around the Package group async updates

Why is this change being made?

Improves guidelines around the Package group async updates. The proposed changes are intended to simplify the existing process:

• Skip repetitive daily updates (when nothing has changed since the last one). These can be overwhelming for those that subscribed for updates. They also generate a long trail of comments, which are not pleasant when scrolling through the issue.

• Prefer updates on issues rather than on the individual related merge requests. Daily updates can become a "recursive" problem for issues with many merge requests. Furthermore, for anyone interested in following the progress, it's much easier to have a single condensed updated on the issue rather than smaller updates spread across multiple merge requests.

• Do weekly async updates on epics ~"workflow::In dev". This is useful to gather the progress across all related issues in a single place (example: gitlab-org&2313 (closed)).

Author Checklist

• Correct MR template applied (e.g blog post)
• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • 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.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.

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