Fix exports in discount-code-importer module

[ajimae]

Summary

Fix issues with modules not exporting directly as default exports in @commercetools/discount-code-importer package.

Completed tasks

• [x] use preconstruct and rollup bundler to bundle module
• [x] remove the direct babel module bunder

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 22b4491eb81f32b7086b37f5aebb28a2ae90fce2

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[codecov[bot]]

Codecov Report

Merging #1879 (804c7ca) into master (2175f68) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 804c7ca differs from pull request most recent head 70b1d22. Consider uploading reports for the commit 70b1d22 to get more accurate results

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  Misses        262      262           
  Partials        3        3