[Story] Fix friend service functionality

[HexaField]

the user-relationship service is currently broken. it needs to be used to store relationships between users.
there are multiple types of relationships, for this issue, we just want to get 'friend' working again

Sub-tasks:

• clean up duplicated code - 1
• fix 'friend' user relationship type functionality - 2
• user invites automatically add user as friend - 1
• add server-core unit tests for the feathers services & feathers listeners - 4

Functionality that needs to be fixed

• create 'friend' type relationship - "Make friend request"
• patch 'friend' type relationship - "Accept friend request"
• remove 'friend' type relationship - "Remove friend"

There is duplicated and commented out code in these files and should be cleaned up appropriately
https://github.com/XRFoundation/XREngine/tree/dev/packages/client-core/src/user/services/UserService.ts
https://github.com/XRFoundation/XREngine/tree/dev/packages/client-core/src/social/services/FriendService.ts