Allow more capable steps that can be reused

At the moment all the steps are limited to a list of commands that can be run. While useful, a more powerful solution would be to allow other types of scripts. An example of this would be an AWS Lambda step where you only have to provide your settings and everything else is already done for you. Currently you need to go through several steps, which includes adding a script to your repository, and that's not an optimal solution.

An example of how this works in a different CI tool is this step that I created for Lambda deployments. Especially the ability to share steps like this across your projects (or with other people), would make Pipelines even more powerful.

Obviously, this would depend on BCLOUD-12750