[Docs] High level overview on URL recommendations and how state containers plays a role

[stacey-gammon]

In order to help plugin developers prefer one way to do things, we should add documentation around best practices regarding URL handling and where state containers and state syncing utilities fits into the picture.

Specifically I think we need to address when using these utilities makes sense (e.g. if an app follows the historical pattern of storing app state in _a and global state in _g), and when it doesn't.

Some questions I can think of:

• If an app stores a minimal amount of state in the url, does it need to use these utilities at all, or should it use native react URL handling?
• Should an app choose state containers over redux, if so why or in what circumstances?

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)