Pass arguments to docker-run.sh on to mautrix-signal

[BVollmerhaus]

The mautrix-signal binary provides a few command line flags to modify its behavior, most recently --ignore-unsupported-server as a workaround to make it function with Dendrite (at least its current main branch). However, setting these options when using the Docker image is not very straightforward. One would have to override the image's CMD to explicitly invoke mautrix-signal with arguments, but that also means losing the registration generation and such that docker-run.sh usually takes care of.

A solution for this would be to have the docker-run.sh script pass any additional arguments on to the mautrix-signal invocation within it. Additionally, it may make sense to invoke the script via ENTRYPOINT instead of CMD so that the latter can be used solely for user-provided args, but being able to override CMD as e.g. ["/docker-run.sh", "--ignore-unsupported-server"] would suffice.

Alternatively, mautrix could also provide environment variables for setting these options.