[Enhancement] Create annotation in K-NN plugin to measure the execution time and logging k-nn Stats

[navneet1v]

Description

Currently in k-NN code base we time different functions like graph creation etc, and also we put some stats in k-NN stats api related to different invocations of different code path. To achieve this we have duplicated code all over the place.

To make it easier we can build some custom annotation in java that can do this work for us and which can be reused at different place.

Some annotation that I am thinking:

1. @LogExecutionTime
2. @EmitStats(name="FaissInit")

There can be many more.