add rendering of ref.name

[gschei]

Description of your changes

The function-extra-resources misses an important feature: to dynamically select a specific secret which was created by a previous step of the composition pipeline. Example

1. I create an S3 bucket, create credentials to access it and store the credentials in a Secret in Namespace "crossplane-system"
2. I want to forward these credentials into a target cluster so they can access that bucket.

Therefore I need the ability to reference a secret by a custom name. Currently the name

ref:
  name: mysecret

must be hardcoded and cannot be set dynamically.

instead I would like to reference it like this:

ref:
  name: {{ .observed.composite.resource.spec.parameters.name }}-mysecret

So I can dynamically load exactly one secret.

I successfully tested the solution below.