ops: Improve GCP support priority for the new Gitaly fleet project structure

During incident (INC-649), we encountered a significant operational issue with the new Gitaly fleet project structure. When investigating our initial hypothesis of a GCP host networking issue, we attempted to submit a support ticket to GCP but discovered that the new project structure didn't provide sufficient support priority. This limitation delayed our incident response and could have extended our resolution time had the root cause actually been related to GCP infrastructure.

The Gitaly fleet has recently moved to a new project structure where VMs are distributed across multiple GCP projects. While this distribution may offer certain benefits, it has inadvertently reduced our ability to quickly engage GCP support during critical incidents. For a service as critical as Gitaly, which directly impacts customers' ability to access their Git repositories, we need to ensure we have appropriate support levels.

We need to:

1. Evaluate the current support priority levels for all GCP projects containing Gitaly hosts
2. Determine the appropriate support priority level needed for Gitaly infrastructure
3. Update the GCP project configuration to ensure adequate support access
4. Document the process for engaging GCP support for Gitaly-related issues

Addressing this gap will ensure we can quickly engage external support when needed during future incidents.