Register an array of action objects to create HTTP endpoints backed by Firestore CRUD operations, then start the Express server.
Pass an array of action objects to addActions. Each action maps an HTTP endpoint to a Firestore CRUD operation. After registering all actions, addActions starts the Express server.
URL parameter name (e.g., "id" for a route like /api/users/:id).
Required for PUT, PATCH, and DELETE. Optional for GET — when provided,
the endpoint performs a single-document lookup instead of a list query.