Incorporate tekton/catalog recommendations

Tekton has a nice document with recommendations for Task authors: https://github.com/tektoncd/catalog/blob/main/recommendations.md we should incorporate the suggestions in this project.

Most importantly is [this one that deals with string interpolation of params](https://github.com/tektoncd/catalog/blob/main/recommendations.md#dont-use-interpolation-in-scripts-or-string-arguments), we need to address this in our tasks.