Automatic merge from submit-queue (batch tested with PRs 46501, 45944, 46473)

Enable the ip-masq-agent on GCE installs

Setting this will trigger cluster/addons/ip-masq-agent/ip-masq-agent.yaml to be installed as an addon, which disable configure IP masquerade for all of RFC1918, rather
than just 10.0/8.

Because the flag defaulted to 10.0/8 we can't just change the default.  I think anyone who needs IP masquerade set up should probably use this instead.

@justinsb @kubernetes/sig-cluster-lifecycle-misc 

Fixes #11204

@dnardo - any reason not to do this?

Release Note:
```release-note

GCE installs will now avoid IP masquerade for all RFC-1918 IP blocks, rather than just 10.0.0.0/8.  This means that clusters can
be created in 192.168.0.0./16 and 172.16.0.0/12 while preserving the container IPs (which would be lost before).
```