feat(relayer): flags for processing and indexing minimum amounts

[cyberhorsey]

This will let us filter out permanently from being added to the queue, messages where:

• a fee is set but it will never be profitable
• a fee is set at a low gas price, and our minimum is now bumped
• a unprofitable message that has circulated the queue too long and is being re-crawled by our crawler over and over

this PR also handles context.Cancelled shutdown error correctly, by doing nothing with the message, instead of Nacking it. Now it will automatically go to a diff consumer.