Merge pull request #6444 from metabase/postgres-enum-support

src/metabase/driver/postgres.clj

src/metabase/query_processor/annotate.clj

src/metabase/query_processor/interface.clj

src/metabase/query_processor/middleware/resolve.clj

src/metabase/types.clj

src/metabase/util/honeysql_extensions.clj

test/metabase/driver/postgres_test.clj

test/metabase/query_processor/expand_resolve_test.clj