Allow specified resource types and names for kube-objects collector

[peterbom]

Addresses #187

As well as using the resource type from the <namespace>/<resource-type> values in the DIAGNOSTIC_KUBEOBJECTS_LIST environment variable, this also allows specifying individual resources with an extra /, e.g. <namespace>/<resource-type>/<resource-name> (because the az CLI examples claim that behaviour).

This also adds a number of automated tests to cover the behaviour being fixed.

[codecov-commenter]

Codecov Report

Merging #188 (122b6b9) into master (9030f55) will increase coverage by 0.63%.
The diff coverage is 84.09%.

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
+ Coverage   78.82%   79.45%   +0.63%     
==========================================
  Files          13       13              
  Lines         713      740      +27     
==========================================
+ Hits          562      588      +26     
- Misses         92       93       +1     
  Partials       59       59              

Impacted Files	Coverage Δ
pkg/collector/kubeobjects_collector.go	88.13% <84.09%> (+6.88%)	⬆️

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[Tatsinnit]

👍 thank you!