Support for the WATCH act

[prometherion]

First, awesome project! 👏🏻

I saw from the configuration file that k-bench can define the actions for the benchmark. In most of the examples out there, CREATE, LIST, GET, DELETE, and UPDATE are used: wondering if there's support also for the WATCH one.

The reason behind that is that I'm using an etcd shim and need to be sure that the watch events that would be faked since not supported natively by the datastore are performing as expected.

I tried to take a look in the code base and wasn't able to find anything so far.