We used to pass the shared secret for double-puppeting via a
`login_shared_secret` parameter, which doesn't seem to exist anymore.
The proper way to do it is via `login_shared_secret_map`.

The comments for `login_shared_secret_map` seem to indicate that it's
only usable with the shared-secret-auth password provider.

However, this bridge is based on mautrix-python (`>=0.20.5,<0.21`) as
per its `requirements.txt`
Support for double-puppeting via arbitrary access tokens landed in
mautrix-python 0.20.1 (6f25b62e80/CHANGELOG.md (L44-L53),)
so it should be possible to use appservice double-puppet.
Related to af04ca1238

A bunch of other parameters seem to have moved around as well.

This patch introduces some new Ansible variables for controlling
additional settings related to encryption, etc.