Add ability to pass configuration from secret

[timchenko-a]

Resolves #9
Implementation is similar to yamlApplicationConfigConfigMap approach.
Maybe in the future it will make sense to review the approach a little bit, because right now it's possible to pass simultaneously yamlApplicationConfig, yamlApplicationConfigConfigMap and yamlApplicationConfigSecret, they all will be handled correctly, but only one of them will be actually used as a config file for the application (due to if/else here). IMHO this might be not really obvious.

I suspect I should also upgrade the documentation here?

Tested locally, worked without any issues:

helm ls
NAME    	NAMESPACE	REVISION	UPDATED                             	STATUS  	CHART         	APP VERSION
kafka-ui	kafka-ui 	2       	2024-04-19 14:45:11.72722 +0300 EEST	deployed	kafka-ui-1.3.0	v1.0.0

helm get values kafka-ui
USER-SUPPLIED VALUES:
resources:
  limits:
    memory: 512Mi
  requests:
    cpu: 200m
    memory: 512Mi
yamlApplicationConfigSecret:
  keyName: config.yaml
  name: kafka-ui-config

Application is also working and reachable.

[azatsafin]

thanks for your proposal and efforts