[grafana] feat: adds multi-org support to sidecar dashboards

[mango-matt]

converts sidecar.dashboards.provider to a list at
sidecar.dashboards.providers allowing the definition of multiple
providers that can be mappped to orgs as required.

still supports the singular variant to retain backwards compatibility
and will prepend it to any configured providers

Results in multi-org support defining providers like the example below which

sidecar:
    dashboards:
      enabled: true
      providers:
        - name: prod
          orgid: 1
        - name: nonprod
          orgid: 2
        - name: ops
          orgid: 3

This then allows dashboard configmaps to be define the annotation k8s-sidecar-target-directory: /tmp/dashboards/ops instructing the sidecar to put the dashboard in the folder that's been specific in our configuration above.

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-dashboard
  namespace: monitoring
  labels:
    grafana_dashboard: '1'
  annotations:
    k8s-sidecar-target-directory: /tmp/dashboards/ops/
data:
  my-dashboard.json: |-
   {}

[CLAassistant]

All committers have signed the CLA.

[mango-matt]

closing as have been made aware that multi-org features are not being pursued