Add egress in agent configuration

Issue: Docs: Update gitlab-remote-development-docs to ... (gitlab-org/gitlab#431142 - closed)

Dependent on - Use network policy egress of remote development... (gitlab-org/gitlab!136286 - merged)

Currently, we cannot have network_policy enabled locally on GDK. This is because GDK runs on a private IP(172.16.123.1) and be default we block access to private IP when network_policy is enabled. With changes in Use network policy egress of remote development... (gitlab-org/gitlab!136286 - merged) , it is now possible to configure the egress rules.

This MR adds the GDK private IP to the allow list so that it can successfully clone the project.