Update GitLab escalations process to include a slack escalations channel for awareness

Currently, escalations are managed within the specific account channel or support channel. Some escalations are posted into e-group channel. This would be a channel dedicated to escalations to build awareness. This is for communication only and is NOT intended to replace account or support channels where escalations are initiated and managed.

Feedback is appreciated whether this would be valuable for e-group and management (sales, product, engineering, etc.). The channel is setup BTW #escalated_customers and can be viewed.