docs: convert commonjs imports to esm in building an app guides

[zimeg]

Summary

This PR updates the "Building an App" guides to recommend ESM imports following related changes to the sample app in slack-samples/bolt-js-getting-started-app#22.

Notes

• Other pages require similar updates to be consistent in ESM recommendations, but we might explore the efforts of fix: Improve ESM compatibility for named exports #2724 before this!

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[zimeg]

👾 One note for the amazing reviewers but I am open to others!

[zimeg]

👁️‍🗨️ note: This page is moved to match the English translations above so the fallback Quickstart guide appears as expected!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.44%. Comparing base (195a3fb) to head (29f0458).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2736   +/-   ##
=======================================
  Coverage   93.44%   93.44%           
=======================================
  Files          37       37           
  Lines        7675     7675           
  Branches      669      669           
=======================================
  Hits         7172     7172           
  Misses        498      498           
  Partials        5        5           

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[WilliamBergamin]

Nice 💯