change(state): Add block channel metrics, in preparation for block fork metrics

[teor2345]

Motivation

These metrics are part of #5297, but we also needed them to diagnose bugs in PR #5257.

This is a low-risk change that is not a release blocker.
But we might want to merge it to improve sync diagnostics.

Solution

• Add minimum queued block height to metrics
• Add metrics to sent block cache
• Add metrics for the last sent finalized height
• update the grafana dashboard

Review

This PR can merge by itself, it is not required to merge PR #5257.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
• How do you know it works? Does it have tests?

[codecov]

Codecov Report

Merging #5327 (80b8818) into main (a28350e) will increase coverage by 0.04%.
The diff coverage is 75.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5327      +/-   ##
==========================================
+ Coverage   79.16%   79.21%   +0.04%     
==========================================
  Files         308      308              
  Lines       39752    39787      +35     
==========================================
+ Hits        31470    31517      +47     
+ Misses       8282     8270      -12     

[teor2345]

This is a low-risk change that is not a release blocker.
We might want to merge it to improve sync diagnostics.

[arya2]

mempool_requests_for_transactions test failed again (bug #5384):

Message: internal error: entered unreachable code: MempoolTransactionIds requests should always respond Ok(Vec<UnminedTxId>), got Ok(Nil)

https://github.com/ZcashFoundation/zebra/actions/runs/3231180904/jobs/5290771906#step:3:6780

[oxarbitrage]

LGTM