Add a helper function to access composition environment variables

[ezgidemirel]

What problem are you facing?

Currently, we can access composition environment variables like:

env: {{ (index .context "apiextensions.crossplane.io/environment").key1 }} 

However, this is too verbose and can be simplified with a helper function.

How could this Function help solve your problem?

To make it easier to access composition environment variables, we can have a helper function called getCompositionEnvVar. The interface might be like:

env: {{ getCompositionEnvVar . "key1" }}