feat(instrumentation-pg): update to stable semantic conventions

[maryliag]

Which problem is this PR solving?

• Part of Implement stable db semantic conventions opentelemetry-js#5658

Short description of the changes

• Updating span and duration metric to use stable semantic conventions. Using OTEL_SEMCONV_STABILITY_OPT_IN to decide when to send OLD, STABLE or BOTH (see https://opentelemetry.io/docs/specs/semconv/non-normative/db-migration/)

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 89.07%. Comparing base (bcf32cd) to head (54275e8).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/instrumentation-pg/src/utils.ts	88.46%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2881      +/-   ##
==========================================
+ Coverage   89.02%   89.07%   +0.04%     
==========================================
  Files         188      188              
  Lines        9197     9223      +26     
  Branches     1890     1900      +10     
==========================================
+ Hits         8188     8215      +27     
+ Misses       1009     1008       -1     

Files with missing lines	Coverage Δ
packages/instrumentation-pg/src/instrumentation.ts	95.16% <100.00%> (+0.11%)	⬆️
packages/instrumentation-pg/src/internal-types.ts	100.00% <ø> (ø)
packages/instrumentation-pg/src/semconv.ts	100.00% <100.00%> (ø)
packages/instrumentation-pg/src/utils.ts	95.75% <88.46%> (-1.56%)	⬇️

... and 1 file with indirect coverage changes

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[trentm]

Another thing: It would be helpful, I think, to add a "Semantic Conventions" section to the instr-pg README, perhaps modelled after https://github.com/open-telemetry/opentelemetry-js/blob/main/experimental/packages/opentelemetry-instrumentation-http/README.md#semantic-conventions

[maryliag]

Still todo: add semantic conv section on README
Update tests

[maryliag]

@trentm ready for review 😄

[trentm]

Does this have a test that we get the expected attributes for the different values of the OPT_IN envvar?

[trentm]

A few nits. Thanks for slogging through this.