Kafka: PP for consumer context bean

JIRA: https://jira.spring.io/browse/INTEXT-112
https://jira.spring.io/browse/INTEXT-111

 - Avoid using hardcoded bean names for consumer context
 - Remove Integer value topic streams count, instead use string value
   - This will allow placeholder values to be used for `streams` attribute
 - Set `group-id` as a bean name for consumer configuration bean only if
   the group id is specified explicitly. This will allow placeholder values
   not being used as a bean name.
 - Add test cases to verify multiple consumer configurations within the
   same consumer context.

Set consumerConfigurations as propertyValue

Better handling of consumerConfigurations

 - Add getConsumerConfiguration(String groupId) in KafkaConsumerContext
   - Fix tests
 - Add additional test case to check multi consumer contexts

Fix getConsumerConfiguration(groupId)

Polishing