Add registering businesses command to encointer-client docker image

[clangenb]

This currently fails at two steps:

• we can't reach IPFS from within the docker (should be easy to fix)
• registering the business and offerings reads the cid.txt from the pwd, which means that the community must be bootstrapped from within the same container. However, bootstrapping and registering the business requires different arguments, and our docker entry script is too dumb to handle that currently.