Parallel and ordered plugin execution

All plugins are run sequentially. Unless there is a dependency on one tool to complete before the next runs, we can instead run tools in parallel.

Because tools depending on other tools (e.g. helm needs to wait for terraform to finish) is unique to the user, this needs to be configurable from operations repositories.

Once a `weight` has been assigned to each plugin, ordering can be managed using Python's built in [multiprocessing lib](https://docs.python.org/3/library/multiprocessing.html). If the use case expands to become more complex (as parallelism often can), we can explore using a tool like [Spotify's Luigi](https://github.com/spotify/luigi)