feat: add pre-config function

Allows using the in-database configuration without SUPERUSER

test/io/configs/expected/no-defaults-with-db-other-authenticator.config

@@ -1,4 +1,4 @@
-db-anon-role = "other"
+db-anon-role = "pre_config_role"
 db-channel = "postgrest"
 db-channel-enabled = false
 db-extra-search-path = "public,extensions,other"
@@ -13,11 +13,12 @@ db-prepared-statements = false
 db-root-spec = "other_root"
 db-schemas = "test,other_tenant1,other_tenant2"
 db-config = true
+db-pre-config = "postgrest.pre_config"
 db-tx-end = "rollback-allow-override"
 db-uri = "postgresql://"
 db-use-legacy-gucs = false
 jwt-aud = "https://otherexample.org"
-jwt-role-claim-key = ".\"other\".\"role\""
+jwt-role-claim-key = ".\"other\".\"pre_config_role\""
 jwt-secret = "ODERREALLYREALLYREALLYREALLYVERYSAFE"
 jwt-secret-is-base64 = true
 log-level = "info"