Fix memory leak when using mandatory flag in CQs

[lhoguin]

Proposed Changes

When the mandatory flag is used for publishing the channel would keep a lot of state in memory as if it was waiting for confirms, even though publisher confirms were not used. This affects v3.9.x and above and seems to have been introduced by the rabbit_queue_type refactoring.

I have confirmed via PerfTest that the problem is fixed. Example command to reproduce:

make run ARGS="--producers 1 --consumers 1 --flag mandatory --flag persistent --auto-delete false --qos 10 --queue 'q'"

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[michaelklishin]

I could reproduce the leak in master and confirm the fix.

[lhoguin]

I have pushed a fix for rabbitmq-diagnostics memory_breakdown reporting 0 for connection processes and added a small comment in the original commit to explain what is being fixed for future reference (only the commit message of the first commit has changed).

[lhoguin]

I have force pushed again to remove the second commit. I will open a separate PR because that issue also affects 3.8, unlike this PR's original issue.