Add enterprise edition and licensing

[timgl]

Changes

• Add an "ee" folder that is copyrighted (as opposed to our MIT licensed repository)
• You can remove this folder and the system will continue functioning normally, in case you want a purely MIT licensed product.
• Added a section in settings where you can add and manage license keys
• Created a repo and service to create licenses (Internal link to repo to see how to create a new license key).
• Add methods to the User model to expose which features are available (given the plan that is activated)

Checklist

• All querysets/queries filter by Team (if this PR affects any querysets/queries)
• Backend tests (if this PR affects the backend)
• Cypress E2E tests (if this PR affects the front and/or backend)

[timgl]

@jamesefhawkins do you mind checking the changes to the licensing

[mariusandra]

I found two "typos" that could be fixed... and it might be good to run kea-typegen to get types for the new logic. The rest looks good!

Running it with and without the "ee" folder worked. However when running without that folder, the /setup/licenses page would still open when I entered the URL directly. Then it would crash when I tried to use it.

This can absolutely be left for a future PR, but I think we need a way to also split the frontend into the "ee" and "non-ee" parts, possibly moving the /setup/licenses page into a ee/frontend folder.

[timgl]

@mariusandra Yep agree 100%. I don't quite have the webpack wizardry (and we only have a tiny bit of ee frontend code right now). Added #1395, would love your input

[Twixes]

What's the use case for multiple licenses per team?

[timgl]

@Twixes You might add a license that expires, or you might add a license that has a higher plan than the one you currently have. It'll be unlikely you'll have multiple licenses active at once, but at least this gives you the history