feat: allow adding links after span creation

[seemk]

Which problem is this PR solving?

Fixes #4476

Short description of the changes

Adds functions to add span links after span creation.

Additionally deleted the test named should set a link as it did not test anything and was a duplicate of should return ReadableSpan with links.

Type of change

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Existing users implementing the span API will see compilation breakage.

Checklist:

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.83%. Comparing base (2610122) to head (fc9acbc).
Report is 19 commits behind head on main.

❗ Current head fc9acbc differs from pull request most recent head a0047d3. Consider uploading reports for the commit a0047d3 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4536      +/-   ##
==========================================
+ Coverage   90.77%   92.83%   +2.05%     
==========================================
  Files          90      328     +238     
  Lines        1930     9529    +7599     
  Branches      417     2050    +1633     
==========================================
+ Hits         1752     8846    +7094     
- Misses        178      683     +505     

Files	Coverage Δ
api/src/trace/NonRecordingSpan.ts	95.65% <100.00%> (+0.91%)	⬆️
packages/opentelemetry-sdk-trace-base/src/Span.ts	97.59% <100.00%> (+0.09%)	⬆️

... and 244 files with indirect coverage changes

[pichlermarc]

Looks good % changelog nits.
Thanks for working on this. 🙂

I will merge this in when all batched with metrics API changes for the next release (and when all changes-requested reviews are resolved)

[pichlermarc]

@martinkuba friendly ping. 🙂 Is this still blocked from your point of view?

[seemk]

@martinkuba