Exchange Gitlab link with the Service Desk for bug reports

The current flow to report a bug in Tor VPN Beta is to navigate to Help > Report a bug, and then choose between On the Tor Forum or On Gitlab.

@gus has suggested switching Gitlab out for Anon-Ticket, which lets bug reporters create anonymous identifiers on the fly without requiring approval first. This would allow beta testers without Gitlab accounts to post bug reports on Gitlab relatively quickly, although each post still requires approval.

However there are a couple of things we should look into first:

• applications/vpn~~ will need to be added as a listed project on Anon-Ticket.~~
• It would be great if we could specify a URL parameter (or similar) that deep-links to the vpn project after the user creates or logs into their identifier.

As per #335 (comment 3262921), we will trial replacing the existing Gitlab link with one to the Service Desk instead: git+tpo-applications-vpn-1326-issue-@gitlab.torproject.org