fix: schema cache loading before the in-db config (#3670)

Fixes #3660. Load the config after getting the pg version but before loading the schema.

The regression happened on f09655b.

Also remove schema cache load wrapper and separate db queries in different functions.

Co-authored-by: Laurence Isla <lau.isla.c@gmail.com>

test/io/test_io.py

@@ -1579,3 +1579,20 @@ def test_admin_metrics(defaultenv):
         assert "pgrst_db_pool_waiting" in response.text
         assert "pgrst_db_pool_available" in response.text
         assert "pgrst_db_pool_timeouts_total" in response.text
+
+
+def test_schema_cache_startup_load_with_in_db_config(defaultenv, metapostgrest):
+    "verify that the Schema Cache loads correctly at startup, using the in-db `pgrst.db_schemas` config"
+
+    response = metapostgrest.session.post("/rpc/change_db_schemas_config")
+    assert response.text == ""
+    assert response.status_code == 204
+
+    with run(env=defaultenv) as postgrest:
+        response = postgrest.session.get("/rpc/get_current_schema")
+        assert response.text == '"test"'
+        assert response.status_code == 200
+
+    response = metapostgrest.session.post("/rpc/reset_db_schemas_config")
+    assert response.text == ""
+    assert response.status_code == 204