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/fixtures.sql

@@ -33,6 +33,9 @@ GRANT
 CREATE SCHEMA v1;
 GRANT USAGE ON SCHEMA v1 TO postgrest_test_anonymous;
 
+CREATE SCHEMA test;
+GRANT USAGE ON SCHEMA test TO postgrest_test_anonymous;
+
 CREATE TABLE authors_only ();
 GRANT SELECT ON authors_only TO postgrest_test_author;
 
@@ -226,3 +229,17 @@ $$ language sql;
 create function get_statement_timeout(items) returns text as $$
   select current_setting('statement_timeout', true) as statement_timeout
 $$ language sql;
+
+create function change_db_schemas_config() returns void as $_$
+begin
+  alter role postgrest_test_authenticator set pgrst.db_schemas = 'test';
+end $_$ volatile security definer language plpgsql;
+
+create function reset_db_schemas_config() returns void as $_$
+begin
+  alter role postgrest_test_authenticator reset pgrst.db_schemas;
+end $_$ volatile security definer language plpgsql ;
+
+create function test.get_current_schema() returns text as $$
+  select current_schema()::text;
+$$ language sql;