feat(cli): extendable plugin configuration types

[imhoffd]

See ionic-team/capacitor-plugins#115 for examples of plugin changes necessary for adding to the plugin config types.

App developers will need to add <reference> lines at the beginning of their config files to pull in the config types from each plugin.

Example capacitor.config.ts:

/// <reference types="@capacitor/keyboard" />

import type { CapacitorConfig } from '@capacitor/cli';

const config: CapacitorConfig = {
    appId: "com.capacitorjs.testapp",
    appName: "capacitor-testapp",
    bundledWebRuntime: false,
    webDir: "build",
    plugins: {
        Keyboard: {
            // TODO
        }
    },
    cordova: {}
}

export = config;

[jcesarmobile]

If plugins are a separate thing, does it make sense to have types for their configurations here?
What about 3rd party plugins?
What if a plugin adds a new config option and can’t be used until a new CLI is released?

[imhoffd]

What about 3rd party plugins?

I was thinking about this, and maybe we can do something like declare module '@capacitor/cli' with the types in each plugin. I can play around with this idea. I mostly made this PR to split out these types from the allowlist PR.