Add configurable list of Scopes and permissions server-side for unauthenticated users

[dotsdl]

From recent discussions, there is interest in making it possible to configure a list of default Scopes + read permissions that unauthenticated users of the AlchemiscaleClient would be granted when connecting to an alchemiscale server's user-facing API. This would enable more transparent, open data approaches to alchemiscale use, where result data is immediately publicly-available as it becomes available.

These "public" Scopes would enable anyone using the AlchemiscaleClient to pull AlchemicalNetworks and result data from these "public" Scopes, including archival-quality extracts (see #246).

Requires #43 to support read-only access to Scopes.