[licensing] Add a license page to the admin dashboard

[corneliusludmann]

Add a page to the admin dashboard that shows the installed license with properties (number allowed users, actual users, domain restriction etc.).

[gtsiolis]

This is also a customer request, see #5743 (comment) and relevant discussion (internal). Cc @JohannesLandgraf

Feel free to add this to the 🥯 product design board[1] if this is something we'd like to work on soon. Cc @corneliusludmann

[mrsimonemms]

Proposed approach

The licensor component doesn't currently have any way of reading the license data - at the moment it's "check x is available" and returns a boolean.

1. Add a getLicense type method to the LicenseEvaluator which will return the relevant information (seats, license type, domain etc) from the licensor. This may be the Gitpod, Replicated, default or fallback license depending upon what's loaded/validated. This would also need adding to the C and Golang modules that this talks to
2. Add a "License" section to the dashboard. See this PR for one way of adding a section to the React app

Important: this ticket is only to read the values of the license and will have no write requirement. This may come in #8717, if at all

[nandajavarma]

We should also be able to list the occupied and remaining seats