Rebalance IMOC rotation between Dedicated and DotCom

In the context of Incidents 2.0, it is beneficial that 2 well staffed IMOC rotations exist in GitLab.

Currently IMOC in Dedicated is best effort between 2 managers. In DotCom the rotation (https://gitlab.pagerduty.com/schedules/PK4YI6X) is staffed by 79 users.

The role of Incident Manager should have transferable skills between the 2 rotations, adding the possibility of a cross-rotation extra role, like Comms Lead.

To execute this, we need to:

• Define well the role of Comms Lead and align practices between Dedicated and DotCom,
• Train both rotations on this role (including diffs between Switchboard and StatusPage capabilities). This entails a LevelUp training that addresses both platforms and gives ready to use resources for escalations/comms, etc.
• Find volunteers to staff Dedicated IMOC in the DotCom rotation
• Adjust PagerDuty assignments to rebalance.
• Announce changes widely to all infrastructure.