feat: add "files" to generated package.json

[mdjermanovic]

Adds "files": [ "lib" ] to the generated package.json.

To avoid lint errors:

C:\projects\tmp\tmp\eslint.config.mjs
   1:22  error  "@eslint/js" is not published                   n/no-unpublished-import
   2:24  error  "eslint-plugin-n" is not published              n/no-unpublished-import
   3:26  error  "eslint-plugin-eslint-plugin" is not published  n/no-unpublished-import

And I believe the plugin author would anyway have to add it before publishing.

[nzakas]

LGTM.