feat: add HPA support for cluster checks runners

[tr3mor]

What this PR does / why we need it:

Datadog has a great capability to autodiscover cluster checks ( for us, it is mainly dbm), which enables a great self-service model for the dev teams. The problem is that you need to scale cluster checks manually. Even a simple CPU/RAM HPA will allow the process to be automatic.
This PR introduces a simple HPA template for cluster checks runners. (took https://github.com/DataDog/helm-charts/blob/1344e8c87955221ba8fa639ca4843c8219b8a0bc/charts/observability-pipelines-worker/templates/hpa.yaml as an example).

Special notes for your reviewer:

I may need some help understanding if I need to update any tests. I don't see tests related to cluster check runners and their PDB, for example.

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• Chart Version semver bump label added (use <chartName>/minor-version, <chartName>/patch-version, or <chartName>/no-version-bump)
• For datadog or datadog-operator chart or value changes, update the test baselines (run: make update-test-baselines)

GitHub CI takes care of the below, but are still required:

• Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• CHANGELOG.md has been updated
• Variables are documented in the README.md

[tr3mor]

this is followup to #2045
I will update docs and version if overall changes approved