Custom PostgreSQL schema support for the xcresult processor

The xcresult processor image now honors the same PostgreSQL schema configuration as the rest of the Tuist stack. When you set a custom schema via the Helm postgresql.schema value or the TUIST_DATABASE_SCHEMA environment variable, the processor connects to that schema instead of the default public schema. This lets self-hosted teams run Tuist in environments where the public schema is restricted or disallowed.