fix: esm-compatibility

[flobacher]

When using commitspark in an esm environment where nodejs loads the files without any further processing from dist/esm this was broken due to

1. no package.json with type: module
2. no file-extension on the package-internal imports

This PR should fix that by adding the extensions to the imports.
The ts setting rewriteRelativeImportExtensions: true converts them correctly to js in the output files.

[advancingu]

Hi @flobacher, thank you! How much I love the simplicity of the TS/JS build ecosystem... I assume importing .ts directly is the latest way of doing things? I assume the other packages are then all broken, too, correct?

In any case, I did a few additional changes in branch https://github.com/commitspark/git-adapter-github/tree/fix/esm-build that you could review. Thanks.

[advancingu]

Merged via #10