[schema2sql] insert some constraints into the backend BoundaryConstraint, IntervalBoundConstraint and StaticVocabularyConstraint can be implemented in SQL with CHECK constraints. Next steps, not part of this changeset: - migrations - removing no longer necessary pre-insertion work on the python side - translating backend exception due to constraint violation into ValidationError Note: this means that these constraints can no longer be ignored by disabling integrity hooks. Related to #5154406

[test] run unittest_syncschema with postgresql Lets us test more things, since we can actually do ALTER TABLE.

[test] run unittest_migractions on postgresql sqlite's lack of support for a bunch of alter table functionality means some thing just don't get tested otherwise.

[devtools] Put pg sockets in /tmp Makes for shorter paths (limited by sockaddr_un). Also use the default port, since we're not listening on TCP sockets.