Add method and benchmarks for pooling metric options

[vordimous]

This PR improves the RecordMetrics() allocations using a pool for the metric.AddOption slice.

benchstat main.txt pool.txt:

goos: darwin
goarch: arm64
pkg: go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp/internal/semconv
cpu: Apple M1 Max
                            │  main.txt   │              pool.txt              │
                            │   sec/op    │   sec/op     vs base               │
RecordMetrics/empty-10        4.513n ± 3%   4.620n ± 0%  +2.38% (p=0.037 n=10)
RecordMetrics/nil_meter-10    341.8n ± 1%   330.7n ± 4%  -3.26% (p=0.022 n=10)
RecordMetrics/with_Meter-10   341.1n ± 1%   330.0n ± 1%  -3.27% (p=0.000 n=10)
geomean                       80.74n        79.59n       -1.42%

                            │   main.txt   │              pool.txt               │
                            │     B/op     │    B/op     vs base                 │
RecordMetrics/empty-10        0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
RecordMetrics/nil_meter-10    696.0 ± 0%     680.0 ± 0%  -2.30% (p=0.000 n=10)
RecordMetrics/with_Meter-10   696.0 ± 0%     680.0 ± 0%  -2.30% (p=0.000 n=10)
geomean                                  ²               -1.54%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                            │   main.txt   │               pool.txt               │
                            │  allocs/op   │ allocs/op   vs base                  │
RecordMetrics/empty-10        0.000 ± 0%     0.000 ± 0%        ~ (p=1.000 n=10) ¹
RecordMetrics/nil_meter-10    6.000 ± 0%     5.000 ± 0%  -16.67% (p=0.000 n=10)
RecordMetrics/with_Meter-10   6.000 ± 0%     5.000 ± 0%  -16.67% (p=0.000 n=10)
geomean                                  ²               -11.45%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

Fixes #5968

[vordimous]

@dmathieu I implemented the feedback and followed the BenchmarkCoreWrite() to have each case benchmarked.

I also created the spelling fix PR: #6407

Thank you for all of the feedback and guiding me through the proper ways to implement this change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.8%. Comparing base (378d704) to head (dd9d610).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6394   +/-   ##
=====================================
  Coverage   67.8%   67.8%           
=====================================
  Files        200     200           
  Lines      16635   16641    +6     
=====================================
+ Hits       11291   11297    +6     
  Misses      4999    4999           
  Partials     345     345           

Files with missing lines	Coverage Δ
...entation/net/http/otelhttp/internal/semconv/env.go	91.0% <100.0%> (+0.5%)	⬆️

[dmathieu]

This is starting to look good :)
We will need a changelog entry though.

[pellared]

Thanks for the PR. Can you please update the branch?

[vordimous]

Thanks for the PR. Can you please update the branch?

PR updated to resolve conflicts