Add latency stats around cluster config file operations

[enjoy-binbin]

When the cluster changes, we need to persist the cluster configuration,
and these file IO operations may cause latency.

[codecov]

Codecov Report

Attention: Patch coverage is 84.61538% with 4 lines in your changes missing coverage. Please review.

Project coverage is 70.95%. Comparing base (b207b42) to head (8efc449).
Report is 7 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/cluster_legacy.c	84.61%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1534      +/-   ##
============================================
+ Coverage     70.92%   70.95%   +0.03%     
============================================
  Files           120      120              
  Lines         65004    65055      +51     
============================================
+ Hits          46104    46162      +58     
+ Misses        18900    18893       -7     

Files with missing lines	Coverage Δ
src/cluster_legacy.c	87.14% <84.61%> (+0.44%)	⬆️

... and 16 files with indirect coverage changes

[hpatro]

Could we also add some sanity tests?

[enjoy-binbin]

start_cluster 1 1 {tags {"latency-monitor cluster external:skip needs:latency"} overrides {latency-monitor-threshold 1}} {
    test "Cluster config file latency" {
        puts [r latency latest]
    }
}

i can get this ouput in my local mac, but it is not certain that they will show in CI. Do you have a better idea?

{command 1736483355 1 1} {cluster-config-fsync 1736483355 6 6} {cluster-config-rename 1736483355 1 1} {cluster-config-open 1736483355 1 1} {cluster-config-close 1736483355 1 1} {fork 1736483355 1 1} {cluster-config-dir-fsync 1736483355 5 5}
[ok]: Cluster config file latency (1 ms)

[hpatro]

i can get this ouput in my local mac, but it is not certain that they will show in CI. Do you have a better idea?

Didn't follow. Could you explain why it won't show up in CI?

[enjoy-binbin]

Didn't follow. Could you explain why it won't show up in CI?

If it is 0ms, it will not show up in the tests.