Unclear/non-existent addon dependencies workflow

**Your Godot version:**

Any

**Issue description:**

I'm making lots of addons for the godotlib and my own projects. Some of these addons need another addon to work. Some addons can be used on their own or as part of a 'parent' addon.

What is the most sensible way to do this in godots current state? (not adding any new features)

I think it would be good to start standardising this type of thing now before every addon just makes up their own way. It could be way more modular and tidy if we all stuck to the same system from now.

For example, do I include both addons in separate folders? So that the required 'package' addon comes with the parent addon that uses the package to work..
This seems like the most logical way, but maybe there is some better way to organise addons that require each other.

I can make a PR about this but I feel there needs to be a consensus on the 'official' or recommended way of doing this.

**URL to the documentation page (if already existing):**

ファイル、テスト、エントリーポイントのいずれも指定されていません。まず、依存関係を持つアドオンを整理する公式な方法について合意を形成し、その後、合意したワークフローと想定されるフォルダーまたはパッケージ構成を文書化してください。

索引モデルが issue の本文から書いたものです。