Add tests for JSON-LD generation

[MatthewGidcomb]

We've seen measurable benefits from including JSON-LD metadata in event pages, so it would be wise to add some testing for that functionality.

Unit Testing

• The logic to produce the metadata content is encapsulated in a static class service for which we could easily write straightforward given-this-event-structure-assert-this-JSON-LD-output unit tests. Low effort, high benefit.
• Testing that the event page includes the metadata may be trickier -- I'm not sure how to tap into the mechanism that updates the document head in unit testing. Unknown effort, medium to high benefit.

E2E Testing

• Add a Cypress test, or modify an existing event creation/editing test, to verify that the appropriate JSON-LD metadata is present in the document head on page render. Medium effort, medium to high benefit.

[MatthewGidcomb]

Next step: @MatthewGidcomb will scaffold a test suite, with at least one test showing how to set it up, with notes on other test cases.

[MatthewGidcomb]

Test suite is scaffolded; ready for someone to finish out for their first contribution.