[feat] 2.0: Add plugin to lib.rs with tauri plugin add

[lorenzolewis]

Describe the problem

tauri plugin add updates package.json and Cargo.toml from what I understand, but there's one more friction point for non-Rust devs: adding the plugin initialiser to the builder in lib.rs. tauri plugin add should do this as part of it's logic

Describe the solution you'd like

Example flow for notification plugin:

1. ✅ User runs tauri plugin add notification
2. ✅ Add dependency to package.json and Cargo.toml (I believe this is already done today)
3. 🆕 Add plugin initialiser to lib.rs on the Tauri app builder (not done today)
4. ❓(optional) Prompt the user with "these are the changes to the files that are going to be made, ready to accept them?" or similar (check out the astro add CLI for how they do that)

Alternatives considered

No response

Additional context

• Discussion in the docs repo: feat: added notifications guide tauri-docs#1379 (comment)
• Astro add command: https://docs.astro.build/en/guides/integrations-guide/solid-js/#astro-add-command
• Keep in mind these two ideas:
  • users who never touch Rust (and have the default Tauri rust project), how do we use this to make Tauri more approachable?
  • Plugins are a much larger story in 2.0 than they were in 1.0, any DX improvements we can do that touch them are a huge win

[lorenzolewis]

@amrbashir we talked about this briefly on Discord a while back, do you think this is something we'd be able to get in (and if so would you be the one able to work on it)? I think this is a pretty crucial piece of DX improvement we can get in prior to 2.0

[amrbashir]

It is definitely on my radar but not super urgent atm and could be added at any time later if we couldn't get it before 2.0-beta.

[lorenzolewis]

As long as we can try to slot it before 2.0 stable then that's fine to me. Thanks!