semantic-conventions: include built esm files in package

[t2t2]

Which problem is this PR solving?

While testing ESM in contrib (open-telemetry/opentelemetry-js-contrib#459) I noticed webpack was still using cjs files for @opentelemetry/semantic-conventions, turns out I missed including esm files for this one package in #2112 and webpack was tolerant enough to not warn about it

Short description of the changes

Include esm files in packed @opentelemetry/semantic-conventions

[codecov]

Codecov Report

Merging #2167 (afe8915) into main (329cf92) will not change coverage.
The diff coverage is n/a.

❗ Current head afe8915 differs from pull request most recent head 0358b20. Consider uploading reports for the commit 0358b20 to get more accurate results

@@           Coverage Diff           @@
##             main    #2167   +/-   ##
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  Coverage   92.80%   92.80%           
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  Files         140      140           
  Lines        5002     5002           
  Branches     1029     1029           
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  Hits         4642     4642           
  Misses        360      360           

[dyladan]

changed title from fix to feat, this is not a bug

edit: removed feat also. this isn't really a feature either