[Feature]: Support for XEP-0484 Fast Authentication Streamlining Tokens

[mwild1]

Precondition

• I understood that this template is only for feature requests and not for bug reports

Cross-checked related issues?

• I have cross-checked this overview Overview: Tasks and Issues #322 as well as filtered for related labels https://github.com/monal-im/Monal/labels

Describe your feature

XEP-0484 FAST token authentication is currently missing from Monal, while many other clients already implement it. Support is available in released versions of Prosody and ejabberd.

Using FAST auth reduces round-trips (leading to faster reconnections), and ensures the server can exclude the client from 2FA prompts and "new client" alerts which are triggered when clients authenticate using a password, which helps to keep user accounts secure.

Fixing this issue would fix snikket-im/snikket-server#240 which is being experienced by Monal users connecting to Snikket instances.