Extend Laravel HasMany relationship with KeyBy method

Adds possibility to have related models in many-to-many relationship attached to the parent model by defined key values. Usually it would be related model id.

call:

$users = User::with('groups')->all()

laravel default:

$user->groups = [0 => $group];

New usage with keyBy:

class User extends Model
{
  use HasManyKeyByRelationship;

  public function groups()
  {
    return $this->hasMany(Group::class)->keyBy('id'); // can be string or callable
  }
}

result:

$user->groups = [$group->id => $group];

This is specially useful in case there is a need to manipulate pivot records in mass. Ex: users/groups grid where grid fields are some value in pivot record and not all pivot records exist

@foreach($users as $user)
  @foreach($groups as $group)
    {{optional($user->accesslevels[$group->id])->level}}
  @endforeach
@endforeach