Set different Kafka bootstrap servers for different auth mechanisms

[rospe]

Is your feature request related to a problem? Please describe.
It is currently not possible to use MSK IAM with actions, therefore, we use SCRAM-SHA-512 there. That also means, that the bootstrap servers are different (port 9096 vs port 9098).
Currently, the helm chart does not support setting an alternative bootstrap server.

Describe the solution you'd like
In a best case scenario all services would support MSK IAM. As long as that is not the case, at least support setting alternative bootstrap servers / setting a different to the globally configured one.

Describe alternatives you've considered
I tried not using the global kafka bootstrap server, but setting this at a service level, but this does not work either, because some install steps do not support that.
Overwriting a globally set attribute in a subchart is afaik not possible in helm.