Update Deprecation notices to include how to assess, how to adjust

This is an MVC to update the deprecation notices to include the how to assess and how to adjust fields gathered recently in the product issue - #5541 (closed)

Problem

The deprecations page is the single source of truth SSoT for breaking changes, deprecations and removals that flow into GitLab. The page currently highlights each breaking change and allows users to filter based on the expected removal milestone.

Each deprecation does not necessarily include steps/guides on how to assess for impact as well as how to adjust if you are a user. This means that the deprecation notices are not always actionable

MVC

Update the description section in the deprecation notices that have been identified as high impact and reaching a lot of customers:

• add subhead "how to assess" and details from gdoc
• add subhead "how to adjust" and details from gdoc

Review from each product section/stage likely necessary for MR merge

/cc @mbruemmer @fzimmer