Add `Release Prep - Tor VPN.md` issue template

With #41522 (closed) we'll be using Mullvad/Tor Browser signing scripts to sign Tor VPN releases.

We should add an issue template similar to Mullvad/Tor Browser ones, with the steps to publish a Tor VPN release.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information

Add Release Prep - Tor VPN.md issue template