add method tag for metadata access monitoring

[shichanglin5]

a label(method anme) is added to the opDist metrics collector of metadata operations at pkg/meta/base.go:217

so that we can clearly view the time duration and qps of different methods through monitoring, which is useful for troubleshooting problems and analyzing performance bottlenecks.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (d95ad52) 56.51% compared to head (7025ea9) 56.53%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3501      +/-   ##
==========================================
+ Coverage   56.51%   56.53%   +0.01%     
==========================================
  Files         149      149              
  Lines       36306    36321      +15     
==========================================
+ Hits        20520    20535      +15     
  Misses      13543    13543              
  Partials     2243     2243              

Impacted Files	Coverage Δ
pkg/meta/base.go	63.89% <100.00%> (ø)
pkg/meta/redis.go	66.93% <100.00%> (ø)
pkg/meta/sql.go	58.53% <100.00%> (-0.13%)	⬇️
pkg/meta/tkv.go	71.57% <100.00%> (-0.11%)	⬇️
pkg/vfs/internal.go	50.00% <100.00%> (+1.73%)	⬆️

... and 8 files with indirect coverage changes

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[SandyXSD]

Usually we use access log and juicefs profile if we want to know details of each operation.

[SandyXSD]

It shall be useful as a history record in prometheus. However, we need fix the display in juicefs stats, since it uses juicefs_meta_ops_durations_histogram_seconds directly there.

[SandyXSD]

@shichanglin5 Could you keep the original opDist (so juicefs stats still works), and add a new HistogramVec for the metrics with tags?

[shichanglin5]

@shichanglin5 Could you keep the original opDist (so juicefs stats still works), and add a new HistogramVec for the metrics with tags?

This way is feasible, but there will be two opDist; How about modifying the stats code and merging the different label statistics of this opDist?