SAMZA-2709: Adding partial update api to Table API

[ajothomas]

Feature:
Samza Table API currently supports PUT, GET and DELETE. Puts typically write/overwrite the data for a key. Users have frequently requested for the ability to perform partial updates i.e update select fields or a part of the record. This PR intends to add update to Table API.

Changes:

• Added updateAsync and updateAllAsync methods to TableWriteFunction and to AsyncReadWriteTable
• All implementations of AsyncReadWriteTable have been changed to accommodate the API change
• Added sendUpdateTo method to MessageStream. Added corresponding operator spec and operator implementation as well

Tests:

• Added tests for changes to all table implementations

API Changes

• TableWriteFunction was earlier using K,V generic types to represent key and record type. With partial updates, U type has been added to represent partial updates which is a backward compatible change
• Similarly, U update generic type was added to AsyncReadWriteTable class generic signature. It affects all implementing classes as well.

[xinyuiscool]

Reviewed 1/3. Continue later.

[xinyuiscool]

The batching impl which is trying to cast the update to the value type is not correct. The fundamental problem is that Operation correctly only contains key and value. We need to add a Update there too to reflect the update operation. For put and get, the getUpdate() will return null. For UpdateOperation. we return null in getValue() but return the correct update in the getUpdate().

[xinyuiscool]

Overall looks look. Some minor things in the comments.

[xinyuiscool]

LGTM! Thanks for all the improvements!

[mynameborat]

Minor follow up on the comments; Looks good otherwise.