Add new QL endpoints of /v2/attr and /v2/attr/{attr_name}

[tzuchen-liu]

[tzuchen-liu]

as for adding test, I plan to add these to the line 126 of tests/clients/test_ngsi_v2_timeseries.py now need to pull in order to commit to another issue, so I put the code here

` entity_attr = client.get_entity_by_attrs( entity_type=self.entity_1.type) for entity in entity_attr: print(entity.to_pandas())

        entity_attr_name = client.get_entity_by_attr_name(
            attr_name="temperature", entity_type=self.entity_1.type)
        for entity in entity_attr_name:
            print(entity.to_pandas())

`

[tstorek]

@SBlechmann is there still any progress on this?

[SBlechmann]

Yes, we are still on it, sorry for the delay.

[SystemsPurge]

@tstorek First , appologies for the long list of commits, only the last three are relevant, the rest stems from a rebase on master because the branch was old. The methods now return the sought after timeseries/timeseries list object. I could not find a way to avoid nested loops, given that the response itself comprises of nested/categorized elements. One important detail : The get_entity_by_attrs method does not combine the timeseries of same entities for different attributes, since extending the values/index for different attributes doesnt seem to be a trivial task : If done properly, the timestamps in the indexes should be compared one by one, to determine whether adding a None value for a specific attribute is necessary. Hence why in the test, as u can see, the method now returns a timeseries list of size : number of unique entities x number of unique attributes. The question then becomes, is it ok for this method to return such a result OR, should a timeseries method be implemented, that combines timeseries of same entities with different attributes?