Consolidate sample projects with Lerna

[khawkins]

As we get more "sub-projects" in the repo—predominantly represented as separate SFDX projects for each set of samples—it would be good to properly configure a top-level project in the hierarchical structure, to allow for consistent application of project maintenance features like linting, formatting standards, etc.

We should:

1. Design a hierarchical project structure, that allows common / collective tasks to be pulled out to top-level project workflows.
2. Leverage Lerna to stitch the hierarchy together, updating all top-level and sub-project configurations as necessary to support this configuration.