Add a rabbitmq.conf setting for two more quorum queue-related keys

[anhanhnguyen]

Proposed Changes

Hi,

We would like to extend the quorum queue configuration under https://www.rabbitmq.com/docs/quorum-queues#configuration to support the INI-style format, allowing the following settings:

quorum_queue.cluster_size = 3
quorum_queue.commands_soft_limit = 32

This aims to provide a more consistent and simplified configuration experience for users.

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[michaelklishin]

Merged manually after renaming one of the options.

Backported manually to v4.1.x.