feat(blooms): Dedupe download queue items to reduce queue size

[cyriltovena]

What this PR does / why we need it:

This PR attempts to avoid enqueueing multiple times the same download request for the same block and reduce the queue size.

The goal is to reduce the size of the queue. I've also changed the behaviour where if the queue is full we just drop the request and we should have a metrics because it might means we need to scale up bloom gateway.

We should test this in dev and see if it has negative impact.

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
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