Segments account escalation opening steps to allow anyone in GitLab to start one

Why is this change being made?

Currently there's a fair bit of back-and-forth between Support and CS when we all know an account escalation should be open... but no one wants to.

This MR:

• adds a note stating that anyone in GitLab can declare an account level escalation
• segments the steps for creating an account level escalation to simplify the process of declaration
• more clearly identifies that only high/critical escalations actually need the escalation tracker doc

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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