Add docs for the env field used in the IQE CJI

[juandspy]

As part of RedHatInsights/clowder#855 a new env field was added to the IQE CJI. I see 2 issues here:

1. It is not clear how to use this new env field. Could you please add one example? For example, as part of CCXDEV-11427, I'm interested in passing DYNACONF_USER_PROVIDER__rbac_enabled=false to the IQE CJI in my pr_check.sh.
2. I can't see the env in the default-iqe-cji.yaml.

[bsquizz]

#329 hopefully serves as a good example -- I'll release those changes next week after testing and confirming that the version of clowder that supports 'env' is running on all environments.

As a follow-up, we may want to add the ability to add some custom additional env vars on the fly with bonfire... a work-around you can use currently is to define your own CJI template file rather than using the default template that ships with bonfire. When you run bonfire deploy-iqe-cji or bonfire process-iqe-cji you can use the --template-file argument:

  --template-file TEXT          Path to ClowdJobInvocation template file
                                (default: use IQE CJI template packaged with
                                bonfire)