add description config option for YAML selectors

[aescay]

Describe the feature

It would be nice to have a description config property available for YAML selectors. Having it natively supported will allow people to access this metadata in from the manifest.json file for other use cases, but it will also support surfacing documentation for selectors in the generated docs!

Describe alternatives you've considered

We could just add a comment in the selectors.yml file, but this won't really allow us to use it anywhere else in the future.

Who will this benefit?

This will benefit teams that have complicated run logic as part of their scheduled jobs. It will also help teams working on larger projects that need to be run in groups to be able to cleanly document their selectors right next to the code used.

Are you interested in contributing this feature?

Happy to help write code or to hash this out more!