Improve DX of adding modules with CLI

[pi0]

Adding common modules is a tedious task especially when you want to make a starter project. There are several ways they can be added:

• The create-nuxt-app approach asks to install them when creating from a template
• Auto-discovery if they are installed in package.json
• Adding with CLI nuxi module add @nuxtjs/color-mode

Using template, is the most common way right now but it has disadvantages:

• Creating a new project takes more time
• Users might not know yet what they need
• Requires templating logic if module addition is not enough

Using auto-discovery is probably the sexiest possible way but it has disadvantages:

• There might be installed dependencies that we do not want as a module
• Needs checking each dependency is a module or not
• We lose the single source of trust about nuxt config

Using CLI:

• Solves template limitation but allowing to do it on demand
• Uses explicit dependency and config (nuxtrc or nuxt.config)
• Allows module authors to define custom (postinstall, postupgrade) hooks by themselves

One more idea I thought with #570, is that we can offer auto install by detecting usage (adding pwa key to nuxt.config or an auto import detected without module). Probably another RFC but worth exploring...

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Notes:

• Legacy RFC: Add nuxt add/rm commands rfcs#31

[Atinux]

I agree that the CLI is the best way for the long run, maintaining create-nuxt-app is already a tedious task and it does not include all the possibilities.

Offering auto-install will be the ice on the cake once we have a strong CLI with nuxi to communicate with the user nuxt config and project dependencies.

[Intevel]

This method has advantages, but I think a comprehensive create-nuxt-app command is good, maybe with example setups for the selectable options.