Add consumers per channel limit

[illotum]

Proposed Changes

This adds a simple per channel limit to the number of consumers. Addresses the raised recently issue with consumer leaks leading to crashes.

It does affect "reply-to" consumers. But doesn't run in rabbit_channel:handle_consuming_queue_down_or_eol. Open to suggestions regarding these cases.

Note that crossing the limit crashes the connection. Same behavior as channel limit, so I figured it's acceptable.

Additionally, fixes a bit of docs and tests for channel_max_per_node.

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)
• Build system and/or CI

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• I have added tests that prove my fix is effective or that my feature works
• All tests pass locally with my changes
• If relevant, I have added necessary documentation to https://github.com/rabbitmq/rabbitmq-website
• If relevant, I have added this change to the first version(s) in release-notes that I expect to introduce it

[michaelklishin]

Merged with a couple of minor changes in #10754.