Update log forwarding tutorial for Loki simplification

With Fluent Bit 1.1.2, there is no need to use a custom secret to control forwarding to Loki - this can be achieved by updating the pod template spec in the cluster config to provide some special annotations: https://docs-staging.couchbase.com/operator/current/tutorial-couchbase-log-forwarding.html#example-loki-stack

As a simple example: https://github.com/couchbase/couchbase-fluent-bit/blob/3c10f93ef47443957edd738bfff72eb9e25ceaef/tools/loki-k8s-stack/values.yaml#L12-L18

      pod:

        metadata:

          annotations:

            # Match all logs

            fluentbit.couchbase.com/loki_match: "*"

            # Send to this SVC

            fluentbit.couchbase.com/loki_host: loki.monitoring

This basically says match all logs (change that wildcard to just what you want, e.g. couchbase.log.audit) and send to that hostname (in cluster but separate namespace here).

Here is an example that creates everything from scratch including the Grafana-Loki stack in a separate namespace: https://github.com/couchbase/couchbase-fluent-bit/tree/main/tools/loki-k8s-stack

You can of course still do a full custom configuration via a K8S Secret. However this approach works with the default configuration and means people don’t need to manage Secrets. It also means we can easily integrate CMOS by just setting those annotations – potentially we could even do this when we deploy CMOS to update the pod specs automatically.

We should highlight this example more heavily across the board as it will be the best way to support CMOS integration as well.