Add config option for enabling local_random_exchange (backport #14348)

[mergify]

Proposed Changes

This adds config option which can be used to prevent creation of local random exchanges. If RabbitMQ is behind a load balancer then local random exchanges can't be used effectively, so it would be useful for operators to set enable_local_random_exchange = false to prevent them from being created.

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• 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)
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• Cosmetic change (whitespace, formatting, etc)
• Build system and/or CI

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This is an automatic backport of pull request #14348 done by Mergify.