client to bridge encryption

**Is your feature request related to a problem? Please describe.**

I want to connect a XMPP MUC with a matrix room having encryption between:

* XMPP clients and the bridge
* Matrix and the bridge

**Describe the solution you'd like**

For example:

* Matrix encryption on the Matrix side
* OMEMO on the XMPP side with blind trust

This is better than having no encryption at all.
Out of scope is a real end to end encryption.

If I am running the bridge on a trusted server it does the job.

**Describe alternatives you've considered**

None

**Additional context**

I am not sure whether this is already possible. If yes, I couldn't find anything about that in the docs.

Start by checking the project documentation for existing encryption support, since the issue says it could not be found there. Then review the current Matrix and XMPP bridge entry points to determine whether encryption is already possible; done would require a defined approach for Matrix-side encryption and OMEMO with blind trust, excluding true end-to-end encryption.

Written by the indexing model from the issue text.