Provide an easy way to check whether a cuds object has certain connections

[yoavnash]

When a user wants to check if a cuds object is connected to another, then he has to use get or item with an additional condition to make the check. get is also inefficient if it results in bringing cuds objects from the backend that are not used.
Could be useful to have a more intuitive method for this. For example, count with filter options.

[yoavnash]

Related to #418

[pablo-de-andres]

Do you want to check if two instances are connected, or if one instance is connected to instances of a certain type?

[yoavnash]

For this we have the get_relationships_between method.
I was thinking of something like cuds.is_connected(rel=..., oclass=...)

[pablo-de-andres]

Then I could rename the issue, since you are not looking for connection to another cuds object specifically
But I agree it would most definitely be useful.

[pablo-de-andres]

I think some relevant methods would be (naming of the methods as a draft):

cuds_object.is_connected(rel=..., oclass=...)  # Check whether cuds_object is connected given the filters
cuds_object.count_connections(rel=..., oclass=...)  # Count the connections from cuds_object given the filters
cuds_object.get_unique(rel=..., oclass=...)  # Returns one object when only one matches the filters, exception otherwise

[yoavnash]

We may want to add a depth parameter to those functions