Enhancement: Add util method within FriendshipManager to check if friend request is sent

[Azeddev28]

Within FrienshipManager, there are two checks:

django-friendship/friendship/models.py

Lines 290 to 298 in 593d63b

	if FriendshipRequest.objects.filter(
	from_user=from_user, to_user=to_user
	).exists():
	raise AlreadyExistsError("You already requested friendship from this user.")
	if FriendshipRequest.objects.filter(
	from_user=to_user, to_user=from_user
	).exists():
	raise AlreadyExistsError("This user already requested friendship from you.")

These validate if a request is sent from a from_user or a to_user. These can be converted into a util method to be used from the FrienshipManager rather than copying these two checks outside of the manager if needed.

I have the util method defined like this

  def check_if_request_sent(self, from_user, to_user):
        if FriendshipRequest.objects.filter(
            from_user=from_user, to_user=to_user
        ).exists():
            raise AlreadyExistsError("You already requested friendship from this user.")

        if FriendshipRequest.objects.filter(
            from_user=to_user, to_user=from_user
        ).exists():
            raise AlreadyExistsError("This user already requested friendship from you.")

Can open a PR, once the idea is approved