fix: kafka health indicator requires kafka configuration

[rorueda]

When no kafka configuration is provided:

Error creating scheduled task for bean [HealthMonitorTask] Failed to inject value for parameter [defaultConfiguration] of class: io.micronaut.configuration.kafka.health.KafkaHealthIndicator

Message: No bean of type [io.micronaut.configuration.kafka.config.KafkaDefaultConfiguration] exists. The following matching beans are disabled by bean requirements: 
* Bean of type [io.micronaut.configuration.kafka.config.KafkaDefaultConfiguration] is disabled because: 
   - Required property [kafka] with value [null] not present