feat(datadog-operator): add ValidatingWebhookConfigurations RBAC

[wdhif]

What this PR does / why we need it:

Adds the necessary RBACs for the Cluster Agent to modify the ValidatingWebhookConfigurations.

This is needed to support the new ValidatingAdmissionWebhook controller in the Agent's Admission Controller.

Special notes for your reviewer:

QA:
For the Datadog Operator Helm Chart:

➜ k describe clusterroles.rbac.authorization.k8s.io datadog-operator
Name:         datadog-operator
Labels:       app.kubernetes.io/instance=datadog-operator
              app.kubernetes.io/managed-by=Helm
              app.kubernetes.io/name=datadog-operator
              app.kubernetes.io/version=1.8.0
              helm.sh/chart=datadog-operator-2.0.1
Annotations:  meta.helm.sh/release-name: datadog-operator
              meta.helm.sh/release-namespace: default
PolicyRule:
  Resources                                                     Non-Resource URLs  Resource Names  Verbs
  ---------                                                     -----------------  --------------  -----
  apiservices.apiregistration.k8s.io                            []                 []              [* list watch]
  mutatingwebhookconfigurations.admissionregistration.k8s.io    []                 []              [*]
  validatingwebhookconfigurations.admissionregistration.k8s.io  []                 []              [*]

Since the Operator that applies the validatingwebhookconfigurations.admissionregistration.k8s.io RBACs to the Cluster Agent is not yet released, the Cluster Agent will not have the correct RBACs, that is expected.

➜  k exec -it deployments/datadog-cluster-agent -- agent status
[...]
====================
Admission Controller
====================

    Webhooks info
    -------------

      ValidatingWebhookConfigurations name: datadog-webhook
      Error: validatingwebhookconfigurations.admissionregistration.k8s.io "datadog-webhook" is forbidden: User "system:serviceaccount:default:datadog-cluster-agent" cannot get resource "validatingwebhookconfigurations" in API group "admissionregistration.k8s.io" at the cluster scope


      MutatingWebhookConfigurations name: datadog-webhook
      Created at: 2024-08-30 13:07:45 +0000 UTC

Checklist

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

• Chart Version bumped
• Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• CHANGELOG.md has been updated
• Variables are documented in the README.md
• For Datadog Operator chart or value changes update the test baselines (run: make update-test-baselines)

[wdhif]

Needed RBACs are implemented in #1555. Closing this PR.