feat: Made PodDisruptionBudget configurable

[houman-moallemi]

What this PR does / why we need it:

Core Issue

At the moment it's not possible to configure the PodDisruptionBudget for the cluster agent. The existing configuration is hardcoded and set to minAvailable: 1 which isn't highly available.

By allowing users to set minAvailable or maxUnavailable we can achieve proper HA in any respective environment.
With this example configuration we can have a highly available cluster agent.

• CA replicas: 3
• PDB maxUnavailable: 1

Interface Consistency

In order to have a consistent interface in the chart, the same changes for clusterAgent are applied to clusterChecksRunner as well. Previous behavior are kept and changes are backwards compatible.

Both createPodDisruptionBudget are copied into the new pdb block so we can deprecate the additional flag in a future minor release.

Special notes for your reviewer:

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