Fix #133 - Endpoint providing microservice config

@Memoized on REST method cannot be done. It cuases following error:
`Caused by: java.lang.IllegalStateException: Ambiguous mapping found. Cannot map 'microserviceConfigurationController' bean method 
protected java.lang.Object com.ofg.infrastructure.healthcheck.MicroserviceConfigurationController.memoizedMethodPriv$getMicroserviceConfiguration()`. However it can be used on internal private method.

In case we'd like to return just content of the file the Content-Type has to be changed from JSON to text plain. When JSON is used the returned value is wrapped into JSON format (but the value itself is treated as pure text data).