Add a cardinality question to the PR template
Add a cardinality question to the PR template

Reviewing a pull request involves assesing in which way the introduced change
affects metrics cardinality. To ease the burder on the reviewer and to make
contributors aware of the constraint, this commit extends the pull request template
with a question about the effect on metrics cardinality.

kubernetes/kube-state-metrics,kubernetes/kube-state-metrics