Design, validate & implement an incentive to contribute in Tails

… for teams that are ready to welcome contributors. For example we could look for translators like this. We could also display this only from time to time and not on every boot.

Related issues

Related to #14559 (closed)

Original created by @u on 15866 (Redmine)

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