Add FAQ for release processes

Why is this change being made?

This is a follow-up from gitlab-org/release/docs!233 (comment 365793900), the release process docs are not very discoverable in the handbook and this is an attempt to make them a bit more prominent and searchable.

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
• 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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mentioned in merge request gitlab-org/release/docs!233 (merged)

@marin I'll assign this to you for review, this is related to our conversation in gitlab-org/release/docs!233 (comment 365793900).

assigned to @marin

marked the checklist item Assign this change to the correct DRI as completed

resolved all threads

approved this merge request

added this merge request to the merge train at position 6

merged

mentioned in commit a5ba88b7

mentioned in issue gitlab-com/gl-infra/scalability#450