fix: Properly configure SDK to be distributed as ESM

[frederikprijck]

Our SDK isnt correctly configured to publish ESM:

• we need to use default, not import
• we need to define type: module in the package.json
• we need to ensure we define file extensions when importing from files

This can cause issues as it may mean certain tools have to rely on auto resolving the module loading and failing as they think our SDK is CJS, but it is ESM.

Solves #1945

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 74.82%. Comparing base (e8f2515) to head (624dc14).

Files with missing lines	Patch %	Lines
src/client/helpers/get-access-token.ts	0.00%	0 Missing and 1 partial ⚠️
src/client/index.ts	0.00%	0 Missing and 1 partial ⚠️
src/server/index.ts	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2028   +/-   ##
=======================================
  Coverage   74.82%   74.82%           
=======================================
  Files          21       21           
  Lines        1863     1863           
  Branches      289      289           
=======================================
  Hits         1394     1394           
  Misses        462      462           
  Partials        7        7           

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