[filebeat][httpjson] - Add min/max template functions

[ShourieG]

This is a request to add min/max template functions for httpjson. Currently no such op exists and adding this will enhance use cases built on top of the input. The min max functions should be able to deal with integers (signed/unsigned) and floating point numbers.

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)