Restore credit_flow between AMQP 0.9.1 channel/MQTT connection -> CQ processes

[gomoripeti]

Proposed Changes

The credit_flow between publishing AMQP 0.9.1 channel (or MQTT
connection) and (non-mirrored) classic queue processes was
unintentionally removed in 4.0 together with anything else related to
CQ mirroring.

By default we restore the 3.x behaviour for non-mirored classic
queues. It is possible to disable flow-control (the earlier 4.0.x
behaviour) with the new env classic_queue_flow_control. In 3.x this
was possible with the config mirroring_flow_control.

Most of the changes are reverted portions of 3bbda5b, except the new function rabbit_misc:process_info/2 and the new test cases classic_queue_SUITE:classic_queue_flow_control_(enabled|disabled)

Fixes #12885

Types of Changes

What types of changes does your code introduce to this project?
Put an x in the boxes that apply

• 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

Put an x in the boxes that apply.
You can also fill these out after creating the PR.
If you're unsure about any of them, don't hesitate to ask on the mailing list.
We're here to help!
This is simply a reminder of what we are going to look for before merging your code.

• 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

Further Comments

[michaelklishin]

web_mqtt_shared_SUITE > mqtt > cluster_size_3 > v4 > flow_classic_queue fails with an undef repeatedly, for example in https://github.com/rabbitmq/rabbitmq-server/actions/runs/12248903112/job/34169379099?pr=12907#step:10:5274

[michaelklishin]

The CI failure fix was a matter of propagating one more test to the mqtt_shared_SUITE f3540ee.

[michaelklishin]

#12907 is green so we can proceed to other stages of reviews and testing the workload from #12885 against this branch.

[gomoripeti]

I did not realise why the shared_SUITE is called shared. I thought it is shared between MQTT v3 and v5.
Thank you, Michael, for fixing it!

[mkuratczyk]

I can no longer reproduce using the code from the issue and I've run a test suite that shows no obvious regressions:
https://grafana.lionhead.rabbitmq.com/goto/NgoPWu4Ng?orgId=1

[michaelklishin]

Merged in #12907. Thank you, @gomoripeti.