[RFC] Using a package manager for plugins

While it's still early days for plugins in Noteplan, it might make sense to keep all the "blessed" plugins in this Github repo, but longer term, that'll start to get untenable. Specially when it comes to releases.

Using a package manager like NPM might make a lot of sense. Using registry.npm.org URLs it's fairly straightforward to search, get details and download packages that can go directly to the Plugins folder.

Here are the benefits to this approach:

1. Third party packages can all follow a naming convention (e.g. noteplan-plugin-commandName) and publish them on NPM and they will become easily discoverable for users.
2. NPM packages have versioning built-in and it will become easy for different plug-ins to be updated independently and for Noteplan to periodically check for updates easily by package name.
3. Since NPM allows for an independent .npmignore file it'll become easy to ignore built files for GitHub and ignore source files for the NPM package. This way Noteplan doesn't have to download any unnecessary files.
4. It should still be valid to use a Github URL to manually download plugins that aren't on NPM. (without all the extra feature though)

Possible downsides:

1. Churn - NPM can be an additive feature so that the churn can be kept to a minimum.
2. it slightly increases the barrier to entry, but it's really just an npm publish command for a plug-in author. For advanced plugins this would be a total win.

この issue では、調査すべきファイル、テスト、エントリーポイントが示されていません。まず、プラグインの検出、ダウンロード、バージョニング、更新、GitHub フォールバックの要件を明確にし、その後、それらの要件を既存のプラグインインストールフローに対応付けてください。合意されたパッケージマネージャーの設計と、テスト可能な動作を含む実装計画ができれば完了です。