Add VPA metrics to kubernetes_state integration

[dturn]

What does this PR do?

Adds the recently added Vertical Pod Autoscaler (VPA) metrics from Kubernetes State Metrics, kubernetes/kube-state-metrics#791, to the ksm integration.

Motivation

We'd like to have these metrics. When we contacted support (https://help.datadoghq.com/hc/en-us/requests/226107) we were informed this was not on the roadmap, so we assumed the next step was to do it ourselves.

Additional Notes

I used the PR that added HPA metrics as a guide #801. I also wasn't sure what metrics I should import, explicitly/implicitly ignore, and if any transformations would be helpful.

Review checklist (to be filled by reviewers)

• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached
• Feature or bugfix must have tests
• Git history must be clean
• If PR adds a configuration option, it must be added to the configuration file.

[dturn]

@hkaj Are you the right person to review this? If not, could you please suggest someone. Thank you.

[ofek]

@dturn Thanks for this! I left a few suggestions that should make the CI pass.