refactor(cli.rs): signer and plugin subcommands, use new clap derive syntax

[JonasKruckenberg]

Replaces runner structs with option structs that implement From<&ArgMatches> / TryFrom<ArgMatches> to clean things up a bit. This makes the code structure more scaleable imo.

This also splits the tauri sign subcommand into two: tauri signer sign and tauri signer generate.

TODO:

• add tauri plugin add subcommand
• update color scheme
• add progress info tauri build
• add progress info tauri dev
• add progress info tauri signer
• add input prompts to tauri plugin init

Notes to self:

enum ResourceDescriptor {
   Semver(Version),
   Registry {
      registry: Option<String>,
      version: Version,
   },
   Git {
      git: String,
      branch: Option<String>,
      commit: Option<String>,
      tag: Option<String>
}

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Docs
• New Binding Issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes. Issue #___
• No

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[lucasfernog]

@JonasKruckenberg I'll merge this PR because we need the clap update and it's a huge refactor already. If you're still interested in doing the other tasks, please open a new PR :) thanks for this amazing work, it really helped migrating to clap 3.0.0-rc.0

[JonasKruckenberg]

Yes it's good to merge as is, I got stuck with the more involved features (that's in part where #3029 originated from) but that will have to continue on a separate branch anyway so 👍🏻 from me