leverage optional okapi dependencies to reduce footprint

Overview

Move all interfaces other than those required for authentication from required to optional

Approach

Pursuant to FOLIO-3253's requirement to implement a "minimal" platform, interfaces not necessary to support authentication should be moved from required to optional. Services relying on such interfaces should return 503 (service unavailable) if their supporting interfaces are unavailable.

Required interfaces include:

• users
• authtoken
• permissions
• login
• configuration

Interfaces that must be moved to optional include:

• service-points
• service-points-users
• password-validator
• notify

Regarding the corresponding business logic updates that need to happen, the preferred approach is to explicitly ask OKAPI if the optional interfaces are available in the current tenant context, then either make the call (or not).

Considerations

mod-users-bl currently supports parameters that allow clients to specify how much information is returned in the response (see https://s3.amazonaws.com/foliodocs/api/mod-users-bl/r/mod-users-bl.html#bl_users_login_post). As discussed, the initial approach we'd like to take here is to maintain support for these, and treat them as "include X,Y, and Z if available". Clients are expected to code defensively and not expect specific data to always be returned just because they've asked for it; they should check, and handle the absence of any required information gracefully.