Chore: Absorb adapt-authoring-usergroups into users module

[taylortom]

Chore

• Merge the adapt-authoring-usergroups module into adapt-authoring-users

Rationale

As part of an ongoing effort to reduce the number of standalone modules (see adapt-security/adapt-authoring-core#112 for prior art), adapt-authoring-usergroups is a strong candidate for absorption.

The module is a single 58-line file (UserGroupsModule.js) that provides a minimal API wrapper for grouping users. User groups are inseparable from user management — they have no standalone purpose and adapt-authoring-usergroups already lists adapt-authoring-users as a peer dependency.

Approach

Following the pattern established in adapt-security/adapt-authoring-core#112:

• Move UserGroupsModule logic into the users module as an internal library class (not an AbstractModule subclass)
• Merge errors.json definitions into the users error definitions
• Merge config schemas into the users config schema
• Merge documentation and doc plugins (jsdoc-style annotations) into users
• Move relevant data schemas into users
• Deprecate the standalone adapt-authoring-usergroups package