Update template with results of API retrospective

• There were a few common themes that came out of the retro from the API service migration into Kubernetes
  • Not all configuration parameters were fully audited
  • Services that we heavily rely upon haven't gone through their own readiness procedure
• Let's call out these items to reinforce or assist the person writing the review of items that could easily be missed
• Also calls out the need to document the differences in how a service may be configured between our various environments
  • It is common to have performance related characteristics to be different due to the size of the environment; let's ensure we document this so the reviewer knows what to expect

Addresses: https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/1750