Add a local flags.ini override file that is not checked in

It would be nice to have a standard flags.ini that is checked in and that shows which flags are available and their default values, and additionally another flags.local.ini that is not checked in, where the developers can override the values in flags.ini.

Later on, it may make sense to remove the flags.ini concept entirely, and replace them with environment variables, there is a tool called direnv that could be used for this, but there may be other options as well.