Update live upgrade assistance to include SE in same region as customer

Why is this change being made?

When reviewing the upgrade plan and doing the pre-scheduling checks, it may help streamline the process if the SE is in the same region as the customer. If they are in different regions, it can take a full day between interactions with the customer (i.e. clarification on architecture, questions in general). This can place a bit of a time crunch on the upgrade assistance.

Additionally, if possible, assign to a SE that will be in the same region as the SE performing the assistance. This will allow of easier communication on context and if questions arise.

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][transparency]
• 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][mr-buddies-slack].
  • 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.

@gitlab-com/support/managers would you be able to review?