Add user client role methods

[phillipfickl]

This PR adds user client role mapping support to the Users resource.

List client roles for a user: Users::retrieveClientRoles($realm, $userId, $clientUuid)
List available client roles: Users::retrieveAvailableClientRoles($realm, $userId, $clientUuid)
Assign client roles to a user: Users::addClientRoles($realm, $userId, RoleCollection $roles, $clientUuid)
Remove client roles from a user: Users::removeClientRoles($realm, $userId, RoleCollection $roles, $clientUuid)

Used endpoints
GET /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}
GET /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}/available
POST /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}
DELETE /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}

[codecov]

Codecov Report

❌ Patch coverage is 0% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.14%. Comparing base (70747c9) to head (9fdff6e).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Resource/Users.php	0.00%	46 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
- Coverage   99.18%   94.14%   -5.05%     
==========================================
  Files          27       27              
  Lines         859      905      +46     
==========================================
  Hits          852      852              
- Misses          7       53      +46     

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[fschmtt]

Hey @phillipfickl thanks for your contribution! 🥳