Handle Field partitioner to pick value from Map structure

[pushpavanthar]

Problem

Field Partitioner could not pick value if the incoming record is of the form of map

Solution

Handled to fetch attribute value when the payload of Map type

Does this solution apply anywhere else?

• [x] yes
• [ ] no

If yes, where?

Test Strategy

Testing done:

• [x] Unit tests
• [x] Integration tests
• [ ] System tests
• [x] Manual tests

Release Plan

[ghost]

@confluentinc It looks like @pushpavanthar just signed our Contributor License Agreement. :+1:

Always at your service,

clabot