feat(state sync): record latency of p2p state requests

[saketh-are]

Analogous to STATE_SYNC_EXTERNAL_PARTS_REQUEST_DELAY metric for centralized state sync.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 71.24%. Comparing base (ad92548) to head (e45b5ea).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
chain/client/src/metrics.rs	0.00%	9 Missing ⚠️
chain/client/src/sync/state/network.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12323      +/-   ##
==========================================
- Coverage   71.25%   71.24%   -0.02%     
==========================================
  Files         838      838              
  Lines      169020   169033      +13     
  Branches   169020   169033      +13     
==========================================
- Hits       120436   120421      -15     
- Misses      43346    43370      +24     
- Partials     5238     5242       +4     

Flag	Coverage Δ
backward-compatibility	0.16% <0.00%> (-0.01%)	⬇️
db-migration	0.16% <0.00%> (-0.01%)	⬇️
genesis-check	1.23% <0.00%> (-0.01%)	⬇️
integration-tests	39.02% <0.00%> (-0.01%)	⬇️
linux	70.69% <0.00%> (-0.01%)	⬇️
linux-nightly	70.82% <0.00%> (-0.02%)	⬇️
macos	50.38% <0.00%> (-0.01%)	⬇️
pytests	1.54% <0.00%> (-0.01%)	⬇️
sanity-checks	1.35% <0.00%> (-0.01%)	⬇️
unittests	64.20% <0.00%> (-0.01%)	⬇️
upgradability	0.21% <0.00%> (-0.01%)	⬇️

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