fixup: add LiveView support

[thecristen]

Summary of changes

Asana Ticket: No ticket

These changes should've been part of the upgrade to Phoenix 1.6 -- it's just some setup and configuration to support LiveView. I mostly followed the steps described in How to Setup Phoenix LiveView. This PR doesn't add any LiveViews or LiveComponents yet :)

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[thecristen]

I have no idea why the package-lock changes so much here.