Experimental quorum queues

[phijor]

This pull request has kind of outgrown its orignial scope.

What this does:

• Unify configuration parsing, by adding a new ConfigParser class
• Manage all queue operations in a central place, the QueueManager.
• Make queue operations less likely to leave the manager in a "zombie state" by using temporary channels. (961c053)
• Allow the use of quorum queues, configurable per-client and per-queue.

TODO:

• document manager, especially how client configuration is parsed and translated into queue setup (2fc0eda, 7f82e03)
• move config into x-metricq subkey (see ConfigParser.top_level_key)
• check that having dashes in config keys (-) are not a problem

  • yep, that's explicitly allowed: the receiver must have a catch-all **kwargs parameter:

    def config(foo, bar, **kwargs):
        assert "with-dash" in kwargs
    
    config(1, 2, **{"with-dash": True})

• do not close temporary channels in background task (here). Await channel closure directly, but log and discard errors that happen when closing. (part of 961c053)
• assign queue names that contain the queue type, like {token}[-{uuid}]-{queue_type}-{role}. This way, changing the queue type and re-declaring a client's queue does not result in errors because of queue argument mismatches. The old queue needs to be deleted by hand though afterwards. (c4ea672)

[bmario]

we should increase the version for this.

[bmario]

Looks good to me, but I found one typo :)

[phijor]

Rebased and ready to merge :)