feat: Add SetKey Support to Expand Processor

[jshlbrd]

Description

• Adds SetKey support to the Expand processor

Motivation and Context

Some data sources have complex object structures with either deeply nested arrays of objects or multiple layers of arrays of objects. For example:

{
    "a": {
        "b": {
            "c": [{
                "d": "e"
            }],
            "h": {
                "i": 1
            }
        }
    },
    "j": {
        "k": 1
    }
}

The processor currently pushes { "d": "e" } to the top of the object like this:

{
    "d": "e",
    "a": {
        "b": {
            "h": {
                "i": 1
            }
        }
    },
    "j": {
        "k": 1
    }
}

This makes it nearly impossible to modify the structure of the object after the processor runs because the content of the array is dynamic. This change adds SetKey support which makes this possible (if the SetKey is "x.y"):

{
    "a": {
        "b": {
            "h": {
                "i": 1
            }
        }
    },
    "j": {
        "k": 1
    },
    "x": {
        "y": {
            "d": "e"
        }
    }
}

This has some other benefits, like making the expansion of non-object arrays possible.

How Has This Been Tested?

Refactored and added new unit tests.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.