add: config db-timezone-enabled for optional querying of timezones

To avoid repeated querying of `pg_timezone_names` every time schema
cache is reset, `Prefer: timezone` can be disabled by setting
`db-timezone-enabled = false`.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

test/io/configs/no-defaults-env.yaml

@@ -20,6 +20,7 @@ PGRST_DB_ROOT_SPEC: openapi_v3
 PGRST_DB_SCHEMAS: multi,   tenant,setup
 PGRST_DB_CONFIG: false
 PGRST_DB_PRE_CONFIG: "postgrest.pre_config"
+PGRST_DB_TIMEZONE_ENABLED: false
 PGRST_DB_TX_END: rollback-allow-override
 PGRST_DB_URI: tmp_db
 PGRST_DB_USE_LEGACY_GUCS: false