configroot: Create "settings" and "modify" files for ipblocklist

configroot: Create "settings" and "modify" files for ipblocklist

The third version of this patch conducts the necessary changes in
configroot. Previously, they took place in ipblocklist itself, which
would have caused user settings to be overwritten, should ipblocklist be
shipped in future Core Updates.

Fixes: #12917
Cc: Stefan Schantl <stefan.schantl@ipfire.org>
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Acked-by: Stefan Schantl <stefan.schantl@ipfire.org>