[telegraf] Support configurable Deployment labels/annotations

[lovetoburnswhen]

Adds the deploymentAnnotations/deploymentLabels properties to values.yaml to allow users to specify custom labels and annotations on the Deployments.

This feature would be tremendously useful for environments that require certain labels to be set - the only alternative would be to fork the chart internally.

---

Tested with:

❯ helm template ./charts/telegraf -s templates/deployment.yaml --set 'deploymentLabels.foo=bar' --set 'deploymentAnnotations.bar=baz'  
---
# Source: telegraf/templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: release-name-telegraf
  labels:
    helm.sh/chart: telegraf-1.8.54
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: telegraf
    app.kubernetes.io/instance: release-name
    foo: bar
  annotations:
    bar: baz
spec:
...

---

• [ ] CHANGELOG.md updated None found
• [x] Rebased/mergable
• [x] Tests pass
• [x] Sign CLA (if not already signed)

[bqbn]

This is a useful feature. One use case is allowing the PodMonitoring resource to have finer granularity in selecting which Telegraf pods to scrape metrics from.

Please consider merging this PR at your earliest convenience.