Add minio client

[brexis]

This pull request update the Dockerfile by installing minio client ant let you run mc commands on the container.

[mimischi]

Thanks for the PR @brexis! I thought mc is a client one can install on their local machine and then manage different remote Minio hosts. Why would one then want to have it in the remote Dokku instance? Do you have a specific use case?

[turicas]

Thanks for the PR @brexis! I thought mc is a client one can install on their local machine and then manage different remote Minio hosts. Why would one then want to have it in the remote Dokku instance? Do you have a specific use case?

I think the idea is to run maintenance tasks directly on the same container, so you're going to execute locally even the network-intensive tasks (like mc cp or mc mirror), which could be very slow on another machine.