Remove ProdOps references from release post template

Why is this change being made?

There are still quite a few references to the Product Operations team in the release post template. This MR suggest to remove them and replace them with references to new DRIs. It also adds some more details on steps that concern deprecation and removal item checks.

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
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  • 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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