Add designated engineer details and adjust wording throughout to updated process

Why is this change being made?

We're incorporating a few changes to help further clarify and define the role of a Support Manager when it comes to Account Escalations. Some of these changes are small but global (change management issues are actively being created for all global changes), and some pertain only to the AMER region.

These changes include:

• (AMER only) Actively trialing having a designated escalations engineer to take technical lead on account escalations for customers in AMER, as they come in.
• (Global change) Add in details on the ZD organization field to indicate if an account is escalated (see https://gitlab.com/gitlab-com/support/support-ops/zendesk-global/triggers/-/issues/70).
• (Global change) Highlight the Escalated Customers project and use of incident issues and retro issues as Support's space to track our progress and work for Account Escalations.

Additionally, wording has been adjusted in an attempt to improve overall clarity.

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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  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
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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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