Implement IP and DNS-based filtering in the HTTP client

*This issue was originally created by [**@sandhose**](https://github.com/sandhose) at .*

The HTTP client can be used to crawl some HTTP resources, like remove JWKS. We want to avoid malicious actors to reach internal endpoints.
We should implement on the DNS resolver level IP and DNS filtering. The default IP blacklist in Synapse could be useful.