Feature: Ability to specify and log slow _percolate calls

[bly2k]

We currently have the capability to log slow queries that exceed a threshold using the following settings:

index.search.slowlog.*

For _percolate calls, it is also possible to run into situations where a we might be interested to know when percolation is having bottlenecks and it would be a nice option to log percolate calls that exceed a threshold just like the above settings for search.

[julianhille]

we also would like to log if a percolation would exceed a certain amount of memory.