Installing Rails: remove Yarn installation and move to JS Bundling lesson

[ZackHoang]

Because

Currently, the link to installing Yarn on the installing Rails project is outdated. Moreover, much of the Rails course does not rely on Yarn until the JS Bundling lesson and later projects if learners wish to bundle JS. This PR removes Yarn installation from the Installing Rails project and move as well as update the Yarn installation guide to JS Bundling lesson so that Yarn will be used where only needed.

This PR

• Remove Yarn installation from Installing Rails project
• Move and update Yarn installation to JS Bundling lesson

Issue

Closes #30977

Additional Information

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