New data source boundary_user

[drewmullen]

The provider currently can only get a user id if the user was created by boundary provider. Thats not possible with the global user

Potential HCL:

data "boundary_user" "globaladmin" {
  name     = "global_admin"
  scope_id = "global"
}

Since boundary user read requires user_id, we'll need to perform a list operation and loop through users till we find the matching login_name. Once the ID is found perform a read and add to the state

If I have sometime next week I will work on this