Add tests for plaintext leaking in logs

[kegsay]

It's very important we don't leak plaintext messages in logs. We should be able to test that stdout/log files do not contain certain sentinel strings. This may require some kind "please enable verbose logging" option in the API.

[poljar]

If you mean that you need such an API in the bindings, you should be able to do this already: https://github.com/matrix-org/matrix-rust-sdk/blob/2a03de3bd5ffd57dc63328964cb430be786d426e/bindings/matrix-sdk-ffi/src/platform.rs#L246-L252.

[kegsay]

I mean the complement-crypto API - most SDKs have the ability to enable trace logging somehow. I use the rust one already.