Allow specifying enableServiceLinks configuration in PodTemplate

[artifactron]

Is your feature request related to a problem? Please describe.
We're running a Kubernetes cluster with 1k+ Service objects, resulting in 5k+ environment variables being injected to pods if enableServiceLinks configuration is set to true, which is also its default value.

Zookeeper and Kafka pods seem can't handle that tremendous amount of environment variables as they keep crashing with no meaningful explanation in the log. Changing enableServiceLinks to false in the Kafka StatefulSet object (by temporarily pausing the operator) fixes the issue, but sure, if the operator is resumed, the configuration will be reverted and Kafka will start to crash.

Describe the solution you'd like
Allow configuring enableServiceLinks in PodTemplate so we can set it to false, resulting in fewer environment variables being injected to the Strimzi-managed pods, which results in working Kafka clusters on the specified cluster.

Describe alternatives you've considered
Allow more flexible schema of PodTemplate so more aspects of Strimzi-managed pods can be configured. An example of an operator that leverages this flexible schema is elastic-operator.

Additional context
N/A

Notifying @raeoks.

[scholzj]

I do not think we plan to support something like the Elastic operator has. But I will have a look at the enableServiceLinks.