Change unit of ops and file-cache latency metrics to microseconds

[kislaykishore]

• ops_latency and file-cache-latency are best represent in microseconds and not millseconds since many operations take less than a millisecond to complete.
• Also change the metric datatype from Float64 to int64.

Description

Now, the operations are appearing in a non-zero latency bucket.

as opposed to the current situation where most operations fall in the zero-bucket:

Same for file-cache:

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - NA
3. Integration tests - NA

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.09%. Comparing base (617168e) to head (e984310).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2380      +/-   ##
==========================================
+ Coverage   79.04%   79.09%   +0.04%     
==========================================
  Files         105      105              
  Lines       11577    11575       -2     
==========================================
+ Hits         9151     9155       +4     
+ Misses       1961     1956       -5     
+ Partials      465      464       -1     

Flag	Coverage Δ
unittests	79.09% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.