feat!: fromFieldPath and toFieldPath

[tenstad]

Description of your changes

Related to https://crossplane.slack.com/archives/C08BBMDCH7W/p1769948003900819

Enables fromFieldPath and reworks into to be toFieldPath, supporting e.g. the following:

        extraResources:
          - kind: Namespace
            apiVersion: v1
            fromFieldPath: metadata.name # only extract metadata.name
            toFieldPath: resources.namespaces # now supports nested structures
            type: Selector
            selector:
              matchLabels:
                - key: foo
                  type: Value
                  value: bar

which would put the following into context:

resources:
  namespaces:
    - kube-system
    - crossplane-system

See commit log for step by step implementation process.

Note: required for #85

I have:

• Read and followed Crossplane's contribution process.
• Added or updated unit tests for my change.

[tenstad]

Closing after #85 (comment). Not desired to break the api to support this.