Create feature-downloads component

[pocmo]

#424 landed the code to expose downloads in engine and session.

For all our apps that want to use Android's download manager for downloads the code will be very similar and we can wrap that in a feature component.

The component will roughly do:

• Subscribe to downloads in the currently selected session (I assume we do not need to subscribe to it in all Sessions?)
• Consume Download objects and pass the data to Androids Download Manager
• Show an optional, customizable UI piece before starting the download (e.g. Download dialog)
• Call back into the app to notify if a download is done (to show some UI)
• Call back into the app to request the Storage permission if needed
• Provide a callback to be called by the app once a permission has been granted (and then it will trigger the download)

┆Issue is synchronized with this Jira Task

[ekager]

Came here to file this! You're always one step ahead 👍

[Amejia481]

This may give us some ideas!
https://blog.novoda.com/download-manager-v2/

[pocmo]

This may give us some ideas!
https://blog.novoda.com/download-manager-v2/

This may be a separate component (or a customization to be added at some later point) though! :)

[Amejia481]

Exactly, this blog post caught my attention because from it we can get some ideas from their learned experiences of creating a similar library.