Need documentation on templating and data manipulation

### What problem are you facing?
I am trying to use the provider with data loaded from a secret using the `{{ secret:namespace:key }}` syntax and I also want to perform some transformations to the data using jq. It is shown that jq can be used in some fields, and the secret injection in some fields. It is not clear which fields jq is applicable on and how it can or can not be combined with the secret injection.

### How could Crossplane help solve your problem?
Some documentation showing what you can and cannot do with more advanced templating in this provider will go a long way.

Read the existing provider documentation for field-level templating, then compare the `{{ secret:namespace:key }}` syntax with the fields that show jq support. Done means clearly documenting which fields support jq, which support secret injection, and whether the two can be combined.

Written by the indexing model from the issue text.