Run Tuist’s Postgres schema outside of public

Self-hosted Tuist deployments can now place their primary Postgres objects in a schema other than public. Configure the schema with the TUIST_DATABASE_SCHEMA environment variable on the server and migration process, or set postgresql.schema in the Helm chart, which propagates the same value into the server, migration job, build processor, and xcresult processor pods. The CNPG grant scripts also accept -v tuist_schema=<schema>. The default stays public, so existing installations are unchanged. This helps environments whose internal database security policies disallow application objects in the public schema, allowing a dedicated, narrowly granted application namespace.