feat: add kyverno functions

[eddycharly]

Explanation

Add kyverno functions.

Fixes #84

[vishal-chdhry]

@eddycharly I see there is a duration datatype now, does this also closes #85?

kyverno-json/pkg/engine/template/kyverno/arithmetic.go

Lines 25 to 27 in 4904d99

	type duration struct {
	time.Duration
	}