Add an internal webhook endpoint for git actions

This is mainly a feature proposal for those of us that host our own GitLab instance.

Using git hooks are okay, but they are synchronous in nature to the developer, eg. when they push, they have to wait potentially minutes for the push to finish.

The GitLab 'Webhooks' are better, as it allows the developer to push and the post-receive actions are done in the background (Asynchronously)

I have the need to run custom actions when a repo is pushed to, so currently I have had to create an endpoint for the webhook, which is simple app behind nginx that runs the actions needed.

Proposal

Build into GitLab an internal webhook endpoint

It should only accepts requests from itself

The app code could either be modified directly within the GitLab interface, or probably better, pulled from a referenced git repo