Support moving nested json to event root

Is your feature request related to a problem? Please describe.
The KeyValue processor writes its output maps to a destination field that is not the root of the event. As far as I'm aware there is not a way to move a nested field like that to the root of the event.

Example event

{message: "key1=val1 key2=val2"}

Current behavior of KeyValue processor

{
   message: "key1=val1 key2=val2",
   parsed_message: {
       key1: "val1",
       key2: "val2"
   }

}

Desired output event

{
   message: "key1=val1 key2=val2",
   key1: "val1",
   key2: "val2"
}

There are other cases beyond the KeyValue Processor where moving a nested field to the event root so building it into a processor would be useful

Describe the solution you'd like
The CopyValue processor should provide an optional parameter like to_root which can copy a field to the event root. It should also support a way of moving all fields within a json object

The configuration to get the desired output from above could look something like this:

  processor:
    - copy_values:
        entries:
        - from_object_key: "parsed_message"
          to_root: true

Describe alternatives you've considered (Optional)
Data Prepper could support something like a Flatten Object processor to flatten nested json.

That config might look something like this

  processor:
    - flatten:
        - key: "parsed_message"

And change the input to be like this

{
   message: "key1=val1 key2=val2",
   parsed_message.key1: "val1",
   parsed_message.key2: "val2"
}

The RenameKey Processor could then be used to get the desired output

Additional context
N/A

Start with the CopyValue processor and compare its behavior with the KeyValue processor's nested destination output. Determine how the requested to_root or object-flattening behavior should be configured, then verify that the example event produces key1 and key2 at the event root without losing the original message.