Support multiple repositories in one instance

[lukaszwawrzyk]

Currently we are just running bazel steward on an existing cloned repository. We could wrap this logic and execute it multiple times on different repositories (first cloning them).

This is useful for companies that just would like to setup 1 job for bazel steward, configure which repositories should it run on and call it done. Without this feature, it would be required to setup a separate job for each project.

Repositories list/file could be a parameter to the Bazel Steward binary. We could accept mixed list of directories and clone urls and run the logic for each of them. By default we would pass as a single relative path (".").