GitLab backs 99.9% availability SLA with service credits

Introduces a 99.9% availability SLA with service credits for Ultimate customers on GitLab.com and GitLab Dedicated. Defines 'downtime minutes' as degraded availability of 5% or more of valid customer requests for covered experiences (Issues, merge requests, Git operations, Container Registry, Package Registry, API requests) resulting in server errors (HTTP 5xx or connection timeouts > 30 seconds). Outlines the process for claiming service credits.