Autogenerate signingkey.jwk on first start if not found?

[poVoq]

When running this via the official docker images it is quite difficult to generate the signingkey.jwk as it is mandatory for the container to start, but there is no way to generate it other than manually installing node on the host system and generating it there from a repo clone.

The best way would be if the container would auto-generate this file if it can't find it at the location configured.

Also the config should probably default to "/data/signingkey.jwk" to avoid confusion with the mounted directory.

Thanks!