nix(test): add test suite for observability tests

- Create separate test suite for observability tests

- Create wrapper script `postgrest-test-observability`

- Add to CI and `postgrest-check`

- Move JWT cache tests under observability tests

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

test/observability/fixtures/privileges.sql

@@ -0,0 +1,9 @@
+-- Schema test objects
+SET search_path = test, pg_catalog;
+
+GRANT USAGE ON SCHEMA test TO postgrest_test_anonymous;
+GRANT ALL PRIVILEGES ON ALL TABLES IN SCHEMA test TO postgrest_test_anonymous;
+REVOKE ALL PRIVILEGES ON TABLE authors_only FROM postgrest_test_anonymous;
+
+GRANT USAGE ON SCHEMA test TO postgrest_test_author;
+GRANT ALL ON TABLE authors_only TO postgrest_test_author;