Support record transformation during consumption

[pcnfernando]

Description:
It would be more efficient during consumption, if Siddhi Source is improved to be configured with transformations to make lightweight message-at-a-time modifications.

For example, if there are 50 fields in a record and user only needs 2 fields to be input to Siddhi, there'll be a performance hit during consumption since mapping is done after consumption of the whole message.

We can refer https://docs.confluent.io/current/connect/transforms/index.html