Migrate to Webpack 5 and Upgrade Node.js to 20

[mmx900]

Context

• Fixes Update app to run on Node 18 or newer (NodeJS 16 has reached End of Support) #682
• To update Node.js, this PR migrates the project from Webpacker to Webpack 5 using jsbundling-rails. Initially, I also tried Shakapacker, but it seemed to require more effort. Since I am not an expert in Webpack (I primarily use importmap-rails at work), I may not be aware of all the considerations. However, if there is a compelling reason to use Shakapacker, I am open to retrying the migration.
• While tests are passing, we need to verify that the bundling works correctly on the production server and in other developers' dev environments.

Summary of Changes

• Following the jsbundling-rails guide, replaced Webpacker with Webpack and jsbundling-rails.
• Following the Webpack migration guide, upgraded Webpack to 5.
• Upgraded Node.js to 20.

Checklist

• Tested Mobile Responsiveness
• Added Unit Tests
• CI Passes
• Deploys to Heroku on test Correctly (Maintainers will handle)
• Added Documentation (Service and Code when required)

Screenshots

Before

After

[DeeDeeG]

Sorry for the delayed response, I will be unavailable to test this until at least the 15th, possible a few days after.

I can spin this up in Docker and see how that goes, and ideally (pay for and run it in) a test Dyno on Heroku.

Thank you for the multiple contributions!