Delivery:System proposed practices and ways of working

Why is this change being made?

During the last quarter we identified some items where the team can improves in ways of working, these items were discussed with the team in gitlab-com/gl-infra/delivery#19481 (closed) and this MR adds them to the Handbook

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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