[Feature]: disable the SASL2 warning on account linking

[lissine0]

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

Currently, SASL2 support is not yet in a prosody release.
(Though the Prosody devs say a release is coming soon)

The warning on account linking should be disabled for now, until the next prosody version is released and admins have a couple of months to update their servers.