[feature] Support schema evolution in a given stream

[nitisht]

As applications evolve, the log events they generate evolve as well. It would be very useful for Parseable server allow schema evolution of a given stream as source applications evolve. This is also reported a as a common issue with ES.

This change would

• further reduce the burden on the user/operator to manage schema
• ensure application's entire life cycle log event data resides on a single Parseable stream, allowing easier analysis
• remove fragmentation of log data across streams

[123vivekr]

Is this being worked on currently?