add whitelist option for igmpproxy

[IgorYbema]

This PR adds the option to configure the whitelist function of igmproxy in the GUI. Whitelisting multicast groups is sometimes necessary in certain situations where the upstream provider blocks if other than expected multicast groups are reported for.

[fichtner]

I'm not against this but it will take too much time to review and test that I can't spare at this time.

[IgorYbema]

Isn't there anyone else who can test and review? By the way, it has been tested by a few users in the Netherlands already and working perfectly

[Staticznld]

Tried this with 24.1.6 and everything is working as expected!