feat(opentelemetry-resources): add schema url

[c-ehrlich]

Which problem is this PR solving?

Resolves #4182

Short description of the changes

The JavaScript SDK, unlike most others, currently does not give the ability to provide a Schema URL to a resource. See: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/resource/sdk.md#resource-creation

This PR implements the ability to provide it.

There was a previous attempt at this by another contributor, which was closed: #5070

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

npm run test

• should create resource with schema URL
• should create resource without schema URL
• should merge resources with schema URL priority given to other resource
• should retain schema URL from base resource when other has no schema URL
• should retain schema URL from the resource that has it when merging
• should have empty schema URL when merging resources with no schema URL
• should handle merging with empty string schema URLs
• should maintain backward compatibility - getSchemaUrl is optional
• should work with async attributes and schema URLs

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[pichlermarc]

thank you for working on this 🙂

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.02%. Comparing base (f2cfd13) to head (9046e4d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5753      +/-   ##
==========================================
+ Coverage   95.01%   95.02%   +0.01%     
==========================================
  Files         303      303              
  Lines        7957     7984      +27     
  Branches     1610     1618       +8     
==========================================
+ Hits         7560     7587      +27     
  Misses        397      397              

Files with missing lines	Coverage Δ
...l/packages/otlp-transformer/src/common/internal.ts	100.00% <100.00%> (ø)
...tal/packages/otlp-transformer/src/logs/internal.ts	100.00% <100.00%> (ø)
.../packages/otlp-transformer/src/metrics/internal.ts	100.00% <100.00%> (ø)
...al/packages/otlp-transformer/src/trace/internal.ts	98.43% <100.00%> (+0.02%)	⬆️
...ckages/opentelemetry-resources/src/ResourceImpl.ts	98.83% <100.00%> (+0.35%)	⬆️

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[pichlermarc]

thanks for addressing the comments, overall this looks good already - just one small blocker left 🙂

[pichlermarc]

I think I'd prefer a readonly property, then use a getter in the ResourceImpl to enforce it, like we do with the other properties to keep it consistent.

cc @dyladan do you have a preference? (since you re-did resources in the latest major version)

[JacksonWeber]

Looks like you might have a duplicated test case between this and the next case.

[JacksonWeber]

You may want to add a negative test to ensure invalid schema URL formats are handled gracefully.