Configure shovels to wait until all sources and destinations are declared (backport #11793)

[mergify]

Proposed Changes

it addresses feature request #10501

Doc's PR => rabbitmq/rabbitmq-website#1987

Dynamic shovels

You can configure the plugin to either always declare the missing source and/or destination queues or instead wait until they are declared, for instance, once the definitions file is imported at node boot up. In the latter case, shovel will try to passively declare the resource until it succeeds. It uses the reconnection_delay to wait between attempts.

To configure the plugin to wait until the resources are available, apply the following configuration to rabbitmq.conf:

shovel.topology.predeclared = true

To configure individual shovels to wait until either the source and/or destination are available, apply these key-pair values to the shovel parameter:

dest-predeclared = true
src-predeclared = true

Shovel parameters take precedence over plugin configuration values.

Static shovels

Static shovels wait until the queue exists provided it is configured with shovel.topology.predeclared = true and the shovel's source has no declarations or it is empty.

Types of Changes

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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

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This is an automatic backport of pull request #11793 done by [Mergify](https://mergify.com).