[FR] Add ActivityPub support.

[RokeJulianLockhart]

Please describe the problem / need you are trying to solve.

I want to be able to subscribe to changes and publish them (publicly and/or privately; it's server-dependent).

Describe the feature or the improvement you'd like and what are you trying to achieve.

Publish activity via ActivityPub.

Describe alternatives you've considered.

Atom, although this doesn't provide any interactive functionality.

Additional context

fediverse.party

[lullis]

Github is still so dominant because of network effects. Most companies and open source projects end up using Github as their main project management tool because so many people are already here.

Having support for ActivityPub would tremendously increase the value of Taiga. Consider this case right here: I am on Github commenting on this issue because the alternative would require me to create an account at tree.taiga.io just to be able to interact with the software team. If Taiga added support for ActivityPub, it would quickly negate this advantage from Github because every Taiga instance would be connected.

Gitlab is also planning to add support for ActivityPub

Implementation-wise: I've recently started working on a library to add ActivityPub support for django applications and I would be more than interested in supporting Taiga to integrate it into the backend.