Add round sync metrics to storage worker

[jberci]

Closes #3088

[codecov]

Codecov Report

Merging #3089 into master will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3089      +/-   ##
==========================================
+ Coverage   68.41%   68.58%   +0.16%     
==========================================
  Files         372      372              
  Lines       36823    36833      +10     
==========================================
+ Hits        25193    25262      +69     
+ Misses       8377     8329      -48     
+ Partials     3253     3242      -11     

Impacted Files	Coverage Δ
go/worker/storage/committee/node.go	70.32% <100.00%> (+0.65%)	⬆️
go/oasis-node/cmd/common/metrics/disk.go	65.51% <0.00%> (-20.69%)	⬇️
go/worker/compute/executor/committee/state.go	85.18% <0.00%> (-14.82%)	⬇️
go/oasis-node/cmd/common/metrics/resource.go	84.00% <0.00%> (-8.00%)	⬇️
go/common/grpc/policy/policy.go	64.38% <0.00%> (-6.85%)	⬇️
go/consensus/tendermint/epochtime/epochtime.go	78.66% <0.00%> (-6.67%)	⬇️
...ompute/txnscheduler/algorithm/batching/batching.go	78.66% <0.00%> (-6.67%)	⬇️
go/storage/metrics.go	75.00% <0.00%> (-3.27%)	⬇️
go/consensus/api/grpc.go	65.85% <0.00%> (-2.44%)	⬇️
go/storage/api/root_cache.go	72.41% <0.00%> (-2.30%)	⬇️
... and 28 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0708e86...713d77f. Read the comment docs.