FR: Inclusion of instance ENV VARs in blueprints

### Description

In blueprints, we sometimes simplify user setup by preconfiguring things like `HOSTNAME` or `APIKEY` etc for our users to create matching env vars as part of getting up-and-running.

If these could be included in the blueprint with _replace_me_ dummy values, the time-to-value is reduced (and user errors/typos are minimised further)

### Epic/Story

_No response_

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate