This is primarily intended for alternative setup UI or where the customisations end up configuring encryption some other way. If used without respecting the warnings in the docs, the user could end up at a blank page - use with caution, and only as directed.
This adds various customisations point in the app for security related
decisions. By default, these do nothing, but would be customised at the
app level via module replacement (so that no changes are needed here in the
SDK).
Fixes https://github.com/vector-im/element-web/issues/15350
