devinfra: add a priority section for support (#8196)

Recently, there's been a case where it was not immediate in the team
that a problem we were dealing with was a P0 for us. This PR intends to
clarify the most common scenarios where for the support handled by the
dev-infra team.

content/departments/engineering/teams/devinfra/index.md

@@ -52,6 +52,19 @@ Find out more about the Developer Infrastructure team's mission, vision, and str
 
 Also see [org-wide areas of ownership](../../dev/process/engineering_ownership.md#developer-experience) and our [team processes](processes.md).
 
+## Support levels
+
+The team operate across a broad range of responsibilities, so it's best to reason in terms of how much a given issue affects others.
+The below list gives an overview of the commonly encountered scenarios, but isn't meant to be exhaustive.
+
+- _P0_: Issues that are affecting at least a third of the engineering team and that have no immediate workaround.
+- _P0_: Issues the CI where a given build is affecting other builds, i.e breaking isolation.
+- _P0_: Issues caused by Bazel, affecting releases (broken release or preventing it to be created).
+- _P1_: Issues with CI or local environment that are threating another team objectives.
+- _P2_: Issues causing intermittent failures in CI.
+- _P3_: Default priorities for support requests when created.
+- _P4_: Issues that can wait, usually QoL improvements.
+
 ## Contact
 
 For **questions** and **discussions** about anything related to developer experience, post a message in the [#discuss-dev-infra channel](https://sourcegraph.slack.com/archives/C01N83PS4TU).