blockForAuth should use the environment for hostname

[coopernetes]

Is your feature request related to a problem? Please describe.
When Git Proxy receives a push, it returns the following message:

remote: GitProxy has received your push ✅
remote:
remote: 🔗 Shareable Link
remote:
remote: http://localhost:8080/admin/push/0000000000000000000000000000000000000000__2e93519910ccf606190680f69a98a97a6c1ead26

When Git Proxy is deployed in a production environment, it should present the hostname of the real server instead of localhost.

Describe the solution you'd like
When Git Proxy receives a push and blocks for approval, it should return a message with the full server's URL. That URL should at least be configurable since there are too many variations of deployment methods.

Additional context
In most environments, Git Proxy will be deployed behind some sort of load balancer and will have a fully-qualified URL to access it as a developer.