feat: add function to retrieve object by path

[nikpivkin]

Ideally, we should point to the location of the misconfiguration in the code as precisely as possible. To do this, the result.new funuction takes an object with its location metadata as the second parameter. But there may be problems with this if the passed input is incomplete.

The following check safely checks for the absence of bar or its false value, but may fail if bar or the parent structure is missing, since the input.provider.foo.bar expression passed to the result.new function will be undefined.

deny contains res if {
  not nput.provider.some_resource.block1.block2.some_attr.value
  result.new(
    "bar does not exist",
    nput.provider.some_resource.block1.block2.some_attr,
  )
}

To solve this problem, we could use the object.get function to safely get a nested object, for example object.get(some_resource, ["block1", "block2", "some_attr"], resource), but in that case the result will not contain the exact location of the misconfig. And calling object.get for each level of nesting is fraught with a lot of code.

This PR adds a function that solves the problem. It recursively searches for a child object along the given path and if it is not found, it returns the last found one.

Example of use:

import data.lib.metadata

deny contains res if {
  not input.provider.some_resource.block1.block2.some_attr
  result.new(
    "bar does not exist",
    metadata.obj_by_path(input.provider.some_resource, ["block1", "block2", "some_attr"]),
  )
}