MM-40813: Use config service more extensively (#19679)

https://mattermost.atlassian.net/browse/MM-40816

```release-note
NONE
```

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/user_test.go

@@ -3542,7 +3542,7 @@ func TestLoginWithLag(t *testing.T) {
 			t.Skipf("requires test flag: -mysql-replica")
 		}
 
-		if *th.App.Srv().Config().SqlSettings.DriverName != model.DatabaseDriverMysql {
+		if *th.App.Config().SqlSettings.DriverName != model.DatabaseDriverMysql {
 			t.Skipf("requires %q database driver", model.DatabaseDriverMysql)
 		}