Common scenario modules

Decomposing GRIT into top-level modules helps manage the complexity of big, overlapping use cases such as Google-GitLab integration and Hosted Runners on AWS. It allows users to replace pieces of GRIT rather than outgrowing the whole thing.

However the most basic, initial configurations looks a little more daunting. There is room for a more simple set of modules that combines the pieces under the hood is a common configuration. We should create such modules as part of GRIT. @tmaczukin calls them "scenarios".

See Add first predefined scenario template (!41 - merged) • Tomasz Maczukin as the initial example and !21 (comment 1754448243) for discussion.