Add PartitionSupervisor

[José Valim]

Processes like Task.Supervisor and DynamicSupervisor can become bottlenecks on large systems and at the moment there is no dead-simple way to parallelize those. A minimal solution takes about 30-50 LOC and I believe it is important for the language to have an out-of-the-box solution to tackle this.

Enter the PartitionSupervisor. I have sent a pull request with examples, docs, and code here: https://github.com/elixir-lang/elixir/pull/11468

[Kenny Evitt]

This seems really interesting, and useful – thanks!

I was curious about any (redacted) details of the kinds of "large systems" for which this would be useful, but the docs in the PR are pretty clear – this is a "dead-simple way to parallelize" dynamic supervisors by running a group of such supervisors, one for each system (CPU) core.