Seniors to be maintainers in 9 months

Why is this change being made?

It is important to keep the maintainer:team member ratio high for throughput and maintainer redundancy.

Under the streamlined Maintainer process it should be possible for a newly hired Senior Engineer to make maintainer in 9 months.

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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