fix(ping): prepend "near_" to metric names

[marcelo-gonzalez]

The ping tool currently crashes when initializing these metrics because the names starting with "near_" is now enforced with a panic

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 71.82%. Comparing base (4fbd40d) to head (9b2c91a).
Report is 20 commits behind head on master.

Files with missing lines	Patch %	Lines
tools/ping/src/metrics.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12219      +/-   ##
==========================================
- Coverage   71.84%   71.82%   -0.02%     
==========================================
  Files         827      827              
  Lines      166624   166624              
  Branches   166624   166624              
==========================================
- Hits       119704   119684      -20     
- Misses      41707    41723      +16     
- Partials     5213     5217       +4     

Flag	Coverage Δ
backward-compatibility	0.17% <0.00%> (ø)
db-migration	0.17% <0.00%> (ø)
genesis-check	1.25% <0.00%> (ø)
integration-tests	38.78% <0.00%> (-0.01%)	⬇️
linux	71.53% <0.00%> (+<0.01%)	⬆️
linux-nightly	71.41% <0.00%> (-0.01%)	⬇️
macos	53.01% <0.00%> (-1.53%)	⬇️
pytests	1.57% <0.00%> (ø)
sanity-checks	1.37% <0.00%> (ø)
unittests	65.64% <0.00%> (-0.02%)	⬇️
upgradability	0.21% <0.00%> (ø)

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