sql: support DEFERRABLE and INITIALLY DEFERRED syntax

Postgres supports DEFERRABLE[1] and INITIALLY DEFERRED[2] syntax. For explicit transactions, deferring them to the COMMIT phase may help performance as we'd do the check in parallel. Others that have cyclical FK dependencies and rely on deferred checks to implement them will have a hard time migrating those workloads to CockroachDB.

[1] https://www.postgresql.org/docs/current/sql-createtable.html#SQL-CREATETABLE-PARMS-DEFERRABLE
[2] https://www.postgresql.org/docs/current/sql-createtable.html#SQL-CREATETABLE-PARMS-INITIALLY

Jira issue: CRDB-57541

Epic CRDB-9559