[FEATURE] Add new resource "btp_*_user"

[lechnerc77]

Currently the assignment of users via the resource btp_*_role_collection_assignment ("*" = globalaccount, directory, subaccount) can trigger the creation of a user in XSUAA if the user is not yet existing there. This flow is intransparenet and can cause confusion.

Therefore we should create a new resource that is basically a copy of the btp_*_role_collection_assignment resource but is called btp_*_user where the user can define a user and a role collection and this way explictly create the user with the assigned role collection. This has a much clearer semantic than the role assignment.

The groups available in the resource btp_*_role_collection_assignment are excluded in the new resource as parameter as you cannot distinguish if a user from the group gets created in XSUAA or not

[lechnerc77]

Moving this to currently out of scope as more investigation is needed and overall architectural discussion is needed for aligning the setup with IAS strategy. Probably worth to revisit in Q4/2024.