Add a debug config that enables the mempool

[teor2345]

Motivation

We want to run acceptance tests on the mempool.

To do that, we need to be able to configure the mempool to start quickly.
(Rather than at the chain tip, which takes hours to sync.)

Closes #2690.

Solution

• Add a mempool debug_enable_at_height config
• Use debug_enable_at_height in the mempool service
• Use debug_enable_at_height in the mempool crawler

Tests:

• Add a basic mempool activation acceptance tests, using debug_enable_at_height

Bug fixes:

• Propagate syncer channel errors through the crawler
• Deny unknown fields and apply defaults for all configs

I'd like to leave the crawler refactor for my next PR, so we can bisect if it causes issues.

Review

@conradoplg can finish off the review for this PR.

This PR is based on PR #2861.

Reviewer Checklist

• Code implements Specs and Designs
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

• Add zebrad acceptance tests for the mempool #2691

Refactor the debug_enable_at_height checks - choose one of:
- move the debug_enable_at_height code into SyncStatus, so we don't have to copy it everywhere we use SyncStatus
- launch the mempool crawler task when the Mempool is enabled, and kill it when it is disabled

[conradoplg]

I rebased this after #2861 was merged.

This seems good, the only thing lacking is already mentioned as TODO (moving flag into SyncStatus to avoid repetition, and tests).

Something that I realized now and may be useful here (or not, feel free to ignore): if we move the crawler inside Mempool, then it won't need to monitor the tip anymore, as it will be enabled/disabled with the mempool (though we'd need logic to re-spawn / kill the task when that happens)

[conradoplg]

(I've just realized that I probably shouldn't have rebased & force-pushed something that it's still a draft, apologies if this makes things a bit difficult on your end @teor2345 😬 )

[teor2345]

(I've just realized that I probably shouldn't have rebased & force-pushed something that it's still a draft, apologies if this makes things a bit difficult on your end @teor2345 😬 )

I don't mind, but I'm glad you mentioned it, so I wasn't surprised when I went to push.
(I probably would have force-pushed my rebase over yours without noticing.)

I can just do git branch -f mempool-debug-config origin/pull/2862/head to pick up your rebase.

[teor2345]

Something that I realized now and may be useful here (or not, feel free to ignore): if we move the crawler inside Mempool, then it won't need to monitor the tip anymore, as it will be enabled/disabled with the mempool (though we'd need logic to re-spawn / kill the task when that happens)

I really like this idea, and I think it could work.

And if we do it, we don't need to modify SyncStatus, because the mempool does the debug activation checks.

[teor2345]

This is now ready for review - I want to do the cleanup in a follow-up PR.

[conradoplg]

Looks good