ref(server): Create extractors for params

[jan-auer]

This creates a new module in objectstore-server that contains all extractors
we need for our web API.

The extractor for the auth-aware service has been moved into this module. This
gives us a cleaner separation between the HTTP layer and the auth logic, which
would even allow us to move that wrapper into a different crate. Additionally,
there are minor changes to it:

• The service no longer has an explicit enforce flag. This is inferred from
  Option and documented on its new constructor.
• We now support case-insensitive parsing of the bearer prefix.

There are also two new extractors for ObjectId and ObjectContext. Endpoints
no longer have to use the Params types directly and also do not have to deal
with configuring the Sentry scope.

This change is a preparation for introducing killswitches.

Ref FS-227

[linear]

FS-227 Add killswitches