Different Confidence thresholds for different entity types

[AchintyaX]

The ListSearchPlugin has a mechanism to remove entities whose match confidence is below a provided threshold.
At there is only one threshold value that can be set, the same threshold value would be applied to filter for all entity types.
The request is to add functionality to allow different thresholds for different entity types.

This requires the following tasks to be done -

1. Update the sample config structure to support the addition of threshold values for different entities
2. Update the confidence filtering mechanism to support changes in config
3. Add needful unit tests to ensure the feature works well.