[$900] Create private fork when a user registers

[jmgasper]

@dhruvit-r - Please see the documentation here, under Next Steps. This is what we'll be working on:

https://github.com/topcoder-platform/topcoder-x-ui/blob/develop/GitlabPrivateChallenge.md

This ticket will track the flow of:

1. A user registers
2. The topcoder-x processor receives the Kafka message to the challenge.action.resource.create with the registration details
3. Topcoder-X looks up the member handle in the Gitlab --> TC mapping table
4. Topcoder-X creates a new private fork of the configured repo
5. Topcoder-X gives the Gitlab member access to the private fork
6. Topcoder-X gives the reviewers access to the private fork (This may be tricky)

That's a very high level flow. We can talk through this a bit more as we get into it and run into issues.

For a sample of how to watch the challenge.action.resource.create queue, have a look at the challenge-forum-processor here: https://github.com/topcoder-platform/challenge-forum-processor

That processor handles the forum flow when a user registers to a challenge, granting them access to the private challenge forum.

Multiple repos

One thing to think about is that some projects have multiple repositories (like a frontend and backend). We'll want to support creating forks / giving access to all those.