Add automatic testing / deployment options

[fordmadox]

...During call-for-comment period, work on adding a few automated workflows to the schema repo (or wait until we change that from "eac-cpf-schema" to "eas-schema"???), for the following purposes:

• Ensure any merge with the development branch passes a set of tests and will not invalidate currently-valid documents (which means we also need a test corpus of valid/invalid documents);
• When anything is merged into the main branch, create a new release build (which will include the deliverables, but not all of the files in the repo).
• etc.