dnsdist: Add rules to be applied on a cache hit

[rgacogne]

• Program: dnsdist
• Issue type: Feature request

Short description

It would be nice to be able to apply actions to responses coming from the cache, for example to be able to log a cache hit to a remote protocol buffer server.

For example:

> rl = newRemoteLogger("192.0.2.1:4242")
> addCacheHitAction(AllRule(), RemoteLogResponseAction(rl))