1. Proposed title of this feature request

Add a control knob to let Logging 6.x vector users choose a CLF behavior between the default vector native one and the one more fluentd compatible.

2. What is the nature and description of the request?

My customer needs a new operation mode in vector CLF that is somewhat compatible with the old fluentd CLF (in which the transferred log is encapsulated in .message dict, rather than merged to the transferred log itself).
In Logging 5.9, there's a PR to align vector CLF's behavior with fluentd CLF. This customer wants a control knob to switch between the old fluentd-compatible behavior introduced in PR 3035 and the vector native behavior (before PR 3035). They need this behavior in Logging 6.0 and later as well.

3. Why does the customer need this? (List the business requirements here)

This customer is an existing Logging 5.9 customer, and they want operational continuity from fluentd CLF to vector CLF across their migrations from Logging 5.9 to 6.0, to 6.1, to 6.2 and so forth. They understand that changing Logging 6.x vector CLF's default behavior affects the other existing users, so they want a selectable switch to choose from the behaviors a la PR 3035 and the default vector way.

4. List any affected packages or components.

cluster-logging-operator

5. Related Support Case and Bugs