Fix additional filter

[stepanstipl]

With the introduction of filtering, we, unfortunately, broke additional kind functionality - #204.

This PR fixes the issue:

$./bin/kubent-darwin-amd64 -a AllowlistedWorkload.v1.auto.gke.io
4:02PM INF >>> Kube No Trouble `kubent` <<<
4:02PM INF version dev (git sha dev)
4:02PM INF Initializing collectors and retrieving data
4:02PM INF Target K8s version is 1.20.8-gke.900
4:02PM INF Retrieved 157 resources from collector name=Cluster
4:02PM INF Retrieved 0 resources from collector name="Helm v2"
4:02PM INF Retrieved 0 resources from collector name="Helm v3"
4:02PM INF Loaded ruleset name=custom.rego.tmpl
4:02PM INF Loaded ruleset name=deprecated-1-16.rego
4:02PM INF Loaded ruleset name=deprecated-1-22.rego
4:02PM INF Loaded ruleset name=deprecated-1-25.rego
__________________________________________________________________________________________
>>> Additional resources (custom) <<<
------------------------------------------------------------------------------------------
KIND                  NAMESPACE     NAME             API_VERSION      REPLACE_WITH (SINCE)
AllowlistedWorkload   <undefined>   cc               auto.gke.io/v1   <na> (<nil>+)
AllowlistedWorkload   <undefined>   datadog-agents   auto.gke.io/v1   <na> (<nil>+)
...

There are some related issues with output formatting discovered (#207), to be fixed separately, and it would be nice to cover this in integration test (#208).