Refactor ES logger for bulk requests

[arvchristos]

This PR is introducing bulk requests for the ES logger, introducing a new parameter called bulk-size and splits the previous url parameter in server and index.

Additionally, a new parameter (flush-interval) is introduced, to flush the ES buffer on a defined period.

[dmachard]

Many thanks for this enhancement :)
It will be nice to clear the buffer also after some time as below

go-dnscollector/loggers/redispub.go

Line 294 in d00bd08

case <-flushTimer.C:

[arvchristos]

Many thanks for this enhancement :) It will be nice to clear the buffer also after some time as below

go-dnscollector/loggers/redispub.go

Line 294 in d00bd08

case <-flushTimer.C:

This is indeed a nice idea. Done :)

[dmachard]

lgtm, thanks!