Make handler flush on reset

[DrLuke]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  CloudWatch implements ResettableInterface (via AbstractHandler), but does nothing on resetting. That means that long running processes like the message consumer don't flush logs between handling messages.

• What is the current behavior? (You can also link to an open issue here)
  Calling reset() on logger doesn't do anything

• What is the new behavior (if this is a feature change)?
  Calling reset() on logger flushes messages

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Other information:

[JerrycheeMM]

Hi DrLuke, may I know how does the reset() being triggered ? I wrote a scheduler script to reset the log every 5 minutes but it seems like its not working. I realized that it is a different set of buffer depending on where the Log::info() is being triggered.

[DrLuke]

@JerrycheeMM See the kernel.reset tag and my specific usecase in the messenger.

[bradp-roweit]

This affects compatability with Laravel Octane too. Octane has a class Laravel\Octane\Listeners\FlushMonologState, which calls the reset() method.

The change in this PR is the same solution we came up with when running into the issue.