CORE-5596 Added extension support to facepalm init.

Added db admin connection spec for use when creating extensions that require super-user privileges.
Refactored the refresh-public-schema call into a function that is executed outside of a transaction, since some extension functions won't be ready for use inside another transaction.
CORE-5596 Added default UUIDs to metadata db cols.
CORE-5596 Fixed file_links primary key.