fix(otlp-transformer): include esm and esnext in package files and update README

[pichlermarc]

Which problem is this PR solving?

Previously the esm and esnext files were not included in the otlp-transformer package even though their corresponding entry points were defined package.json.

This PR also updates the README.md file of this package to drop information about not implemented features.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• existing tests

Checklist:

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

[codecov]

Codecov Report

Merging #2992 (99dd245) into main (bfd04b0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2992   +/-   ##
=======================================
  Coverage   92.71%   92.71%           
=======================================
  Files         183      183           
  Lines        6134     6134           
  Branches     1299     1299           
=======================================
  Hits         5687     5687           
  Misses        447      447