Checklist

• I've searched the issue queue to verify this is not a duplicate feature request.
• I've pasted the output of kargo version, if applicable.
• I've pasted logs, if applicable.

Proposed Feature

I would like to propose a new feature that allows the use of custom bash or script steps in the promotion process. This would enable users to integrate complex scripts that are not currently supported by the existing promotion steps, such as those involving intricate loops and conditional statements.

Motivation

The current promotion steps outlined in the documentation (https://docs.kargo.io/references/promotion-steps/) do not support more complex scripting needs that some users might have, including myself. For example, I have some Python and Bash scripts in my CI that perform tasks more complicated than simply copying a file or updating a YAML file. Allowing custom script steps would provide the flexibility needed to handle these advanced use cases seamlessly within Kargo.

Suggested Implementation

I suggest implementing a new feature that allows users to run custom scripts (e.g., Bash or Python) as part of the promotion process. This could involve adding a new promotion step type where users can specify their script, and Kargo would execute it in the appropriate context. This approach would enable users to leverage existing scripts in their CI/CD pipelines without needing to re-write or significantly modify them to fit into the current promotion step framework.