Increase identified S2 updates frequency

Why is this change being made?

15 minutes felt too soon for identified S2 updates, this MR increases the frequency to post every 30 minutes instead.

Note that in this particular incident, gitlab-com/gl-infra/production#2542 (closed), the resolution was fully dependent on a 3rd party provider and we mostly didn't have much to say, however, this might be different if the resolution is dependent on GitLab solely. I think 30 minutes could be acceptable for identified S2 incidents in all cases.

Author Checklist

• 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][transparency]
• 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][mr-buddies-slack].
  • 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.