Configure a custom Postgres schema via the Helm chart

The Tuist and Kura Helm charts now expose a postgresql.schema value that lets self-hosted deployments run Tuist’s primary Postgres objects in a customer-defined schema instead of public. The value defaults to public, so existing installs behave the same, and it is wired into the server, migration job, build processor, and xcresult processor pod manifests, keeping application code unqualified while placing tables, migrations, and processor/ops grants in the chosen schema.