Cleanly dispose of RabbitMQ connections

[robcarlan-datadog]

Motivation

Seeing some rare ( < 1%) test flakiness where the final topic doesn't appear on the list of checkpoints.

The message seems to be correctly published and consumed, as we see traces from both sides. However, we don't see the checkpoint in the test code.

When looking around I saw that the RabbitMQ connections weren't being disposed of. Potentially, this could fix the flakiness just by virtue of taking longer to close the RabbitMQ connection.

Changes

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