Add support for contains operator

[gkorland]

ref RedisJSON/RedisJSON#494

Checks if a string contains the specified substring (case-sensitive), or an array contains the specified element.

[?(@.name contains 'Alex')]
[?(@.numbers contains 7)]
[?('ABCDEF' contains @.character)]

[gkorland]

It seems like in general many operators are missing like in, nin, subsetof....
see: https://github.com/json-path/JsonPath