Add RequiresVectorsDB and RequiresDocumentsDB traits that probe the
database create endpoint once per test class and call markTestSkipped
when the backend returns a 500 error. This handles CI environments
where COMPOSE_PROFILES only starts a single database service.
Applied to all VectorsDB test classes (need PostgreSQL) and all
DocumentsDB test classes (need MongoDB): main tests, permissions
tests, and transaction tests. Also added a fallback guard in the
shared DatabasesBase::setupDatabase() method.
