Proposal for performance priority labels

Current description

To help clarify priority of issues, from the perspective of their impact on availability and performance of GitLab.com.

Closes https://gitlab.com/gitlab-com/infrastructure/issues/1943

Original description

I do not think this is a priority right now, but it stems from https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/5373/diffs which I broke into smaller merge requests.

source/handbook/engineering/performance/index.html.md

@@ -160,7 +160,7 @@ revision, new revision, and ref (e.g. tag or branch) name.
 1. Sidekiq updates PostgreSQL
 1. Unicorn can now query PostgreSQL.
-### Availability and Performance Priority Labels
+## Availability and Performance Priority Labels
 {: #performance-labels}
 To clarify the priority of issues that relate to GitLab.com's availability and