Add Fluentbit Auth Policies

From @staskiewicz.blane

Hey good morning Andrew, the IB PoPs team reached out to me about adding an istio policy like loki-allow-fluentbit-namespace-policy to loki for fluentbit. It seems like they have to set this in order to fix the fluentbit pods

    istio:
      enabled: true
      hardened:
        enabled: true
        customAuthorizationPolicies: 
        - name: "loki-allow-fluentbit-policy"
          enabled: true
          spec:
            action: ALLOW
            rules:
            - from:
              - source:
                  namespaces:
                  - fluentbit