Support managed storage

[komachi]

Allows to use managed storage to pre-define hostnames. For example, you can save this file as ~/.mozilla/managed-storage/@testpilot-containers.json

{
  "name": "@testpilot-containers",
  "description": "ignored",
  "type": "storage",
  "data": {
    "siteContainerMap@@_en.wikipedia.org": {
      "neverAsk": true,
      "userContextId": "2"
    }
  }
}

And then en.wikipedia.org would be opened in container with id "2".

Not a fix, but related to: #1282 #1427

[dannycolin]

First of all, thanks for contributing. I'm sorry you didn't get an answer earlier! I'm also a volunteer like you and got only recently more involved on Multi-Account Container.

I can't give a timeline nor promise anything but I'm currently working on an API proposal to move the website assignments to Firefox itself. That means supporting the managed storage isn't something we're planning to support directly in Multi-Account Containers.

I will then close this PR but if you have any other feature/bug you'd like to work on, please feel free to get in touch with me directly. You can contact me on our chat platform at https://chat.mozilla.org. There are instructions on how to connect to it on https://wiki.mozilla.org/Matrix.