feat: Adding GO callout for extauthz for block ip and adding callout server and tools

[mateustd-ciandt]

This update introduces functionality for extracting the client IP address from the x-forwarded-for header.

It checks if the client IP falls within a blocked range (e.g. 10.0.0.0/24).

If the IP is blocked: the request will be denied, and the response will include a header x-client-ip-allowed set to false.
If the request is allowed: the response will include a header x-client-ip-allowed set to true.

This functionality is exemplified in two new files: block_ip.go and block_ip_test.go, which include the corresponding logic and tests.

Also adding a callout_server.go and callout_tools.go just like we have for extproc but for extauthz, we will also use this for other examples in the future.

Since this is the first commit for extauthz for GO I'm also adding a Dockerfile, docker-compose and the ssl_creds folder.