Document kratix-pipeline-utility for users

[abangser]

During a customer workshop we were asked about the cost of workflow image building and it was indicated people would get pretty far with a reasonable baseline image + command. With that in mind, when they heard about kratix-pipeline-utility they were interested in understanding more. This could be a low cost way to improve the devex for building easy workflow steps.

Note: Currently it is only mentioned in our workshop docs: https://docs.kratix.io/workshop/part-ii/writing-your-first-promise#workflow

[kirederik]

i dont think the utility-image was thought for public consumption (using it in the workshop just made things easier), so i'd be reticent in documenting it as part of writing a promise.

however, the point that people do not easily get that they can have a single image with all their scripts (or that they can use a base [like alpine] with a bunch of bash under command and args) is worthy highlighting, maybe in a :::tip admonition in the writing a promise 🤔