Implement UNIX socket support for gRPC and HTTP listeners

[hbjydev]

What this PR does:

This PR resolves an issue when trying to set the HTTPListenNetwork or GRPCListenNetwork config values to unix where a port would be appended to the file path, preventing the socket from being bound.

As an example, take this configuration:

server:
  http_listen_network: unix
  http_listen_address: /var/run/http.sock

This would lead to a listener being created for unix:///var/run/http.sock:80, including the default value for the HTTPListenPort, :80.

This PR adds a brief check to see if the network is unix and if so, removes the port from the address, leading to the correct address being bound (unix:///var/run/http.sock).

Which issue(s) this PR fixes:

Fixes #475

Checklist

• Tests updated
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]