Make OTel the default for metrics

[kislaykishore]

Description

Use OTel for metrics by default. One can override the behavior to use OpenCensus instead by setting --enable-otel flag to false.

Link to the issue in case of a bug fix.

b/387898221

Perf impact:

Branch	File Size	Read BW	Write BW	RandRead BW	RandWrite BW
Master	0.25MiB	452.23MiB/s	1.16MiB/s	63.39MiB/s	1.29MiB/s
PR	0.25MiB	465.06MiB/s	1.33MiB/s	65.42MiB/s	1.29MiB/s
Master	48.828MiB	3757.51MiB/s	77.25MiB/s	1176.68MiB/s	79.37MiB/s
PR	48.828MiB	3832.38MiB/s	80.22MiB/s	1209.13MiB/s	81.02MiB/s
Master	976.562MiB	3906.58MiB/s	29.89MiB/s	443.78MiB/s	33.62MiB/s
PR	976.562MiB	3897.71MiB/s	33.91MiB/s	573.08MiB/s	32.56MiB/s

Testing details

1. Manual - Tested the Prometheus endpoint.
2. Unit tests - NA
3. Integration tests - Covered by existing tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.11%. Comparing base (cec1b20) to head (488d6b0).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2859      +/-   ##
==========================================
+ Coverage   76.08%   76.11%   +0.03%     
==========================================
  Files         118      118              
  Lines       16557    16557              
==========================================
+ Hits        12598    12603       +5     
+ Misses       3427     3423       -4     
+ Partials      532      531       -1     

Flag	Coverage Δ
unittests	76.11% <100.00%> (+0.03%)	⬆️

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