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 89.74359% with 4 lines in your changes missing coverage. Please review.

Project coverage is 89.76%. Comparing base (5909ad4) to head (9cf4d66).

Files with missing lines	Patch %	Lines
...node/opentelemetry-instrumentation-pg/src/utils.ts	88.46%	3 Missing ⚠️
...elemetry-instrumentation-pg/src/instrumentation.ts	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2881      +/-   ##
==========================================
+ Coverage   89.53%   89.76%   +0.23%     
==========================================
  Files         182      187       +5     
  Lines        8837     9176     +339     
  Branches     1844     1894      +50     
==========================================
+ Hits         7912     8237     +325     
- Misses        925      939      +14     

Files with missing lines	Coverage Δ
...telemetry-instrumentation-pg/src/internal-types.ts	100.00% <ø> (ø)
...de/opentelemetry-instrumentation-pg/src/semconv.ts	100.00% <100.00%> (ø)
...elemetry-instrumentation-pg/src/instrumentation.ts	94.68% <80.00%> (-0.37%)	⬇️
...node/opentelemetry-instrumentation-pg/src/utils.ts	95.75% <88.46%> (-1.56%)	⬇️

... and 5 files 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 😄