Track anon Users that register

# Track anon Users that register
The work on #1105 and #1038 gets us to track core actions, among the actions, we track when an installation is created from GitHub, However, these installations can sometimes lack a `current_user` as in some cases the user hasn't been to the website or some such case. In that case, we track an anonymous project using the `sender id` in the payload. This `sender id` belongs to a user who could potentially discover the website and join.

I am proposing that we track the `conversion` above that occurs when a user that was previously just tracked from an installation joins the system.

## Subtasks
- [ ] When creating a user from GitHub OAuth we should check to see if their id has been used to create an installation
- [ ] If not then we don't need to track anything
- [ ] If the user's id has indeed been used before we should track this as a conversion from anon to registered

## References

Progress on: #1038