Enhancement: Flogo interceptors should function as 'aspects' that can be attached to flow/activities

[aambhaik]

Case: Transmit Metrics/Logging from the flow without embedding log activities in the flow itself.
Proposal: Can we enhance the interceptors to allow pluggable interceptor aspects, not just attribute overriding. So, log emitter can be one such aspect that can be attached to a flow or activities within the flow.

There can be more than one such aspects that do pre/post processing.