ClusterLogging should manage LokiStack and Elasticsearch in parallel

1. Proposed title of this feature request
ClusterLogging should manage LokiStack and Elasticsearch in parallel

2. What is the nature and description of the request?
While https://access.redhat.com/articles/6991632 is covering the migration from elasticsearch to LokiStack it's missing to highlight that up to OpenShift Container Platform 4 - Cluster Logging 5.6 at least, both LokiStack and elasticsearch can be added to ClusterLogging instance added without noticeable impact.

This becomes handy for enterprise environment, where the transition from elasticsearch to LokiStack will take month rather than days.

Unfortauntely, even when both logstore types are added, only one, specified by type: lokistack for example is managed.

This is creting additional burdon as now, elasticsearch can no longer be managed over the well know/documented procedure (via ClusterLogging instance).

3. Why does the customer need this? (List the business requirements here)
Given that the transition from elasticsearch to LokiStack may take month and even more, it's crucial in enterprise environments to have both stacks managed in parallel, using the ClusterLogging instance.

The reason for this being, that elasticsearch may still require adjustments during this time for example with regards to retention time, resources required or even to add or remove elasticsearch members.

Given that customers have build in most cases a complete automated stack, using GitOps, not being able to now manage both stacks via ClusterLogging instance is introducing additional burdon on the customer, hindering adoption of LokiStack and also requiring changes in the automation, which are expensive and can lead to non expected outcome/behavior.

This is why, enterprise customers request to be able to manage both elasticsearch and LokiStack in parallel at least for the time of the transition. And of course also have ClusterLoggingOperator reconcile all changes to the respective stack.

4. List any affected packages or components.
OpenShift Container Platform 4 - Cluster Logging