Standardize speaker schema and provide export

Problem/Motivation

The EOWG is interested in starting a "speaker bureau". That is, some database (currently just a manually curated sheet) of active speakers so that other events can reach out when they do calls for speakers.

There is currently no standardization on this front and speakers are manually pulled from various event sites. The Event Platform provides a unique opportunity to standardize this data, and provide a way to easily output it.

Steps to reproduce

Look at other Drupal event sites.

Proposed resolution

• Determine a schema for speakers, potentially a subset of https://schema.org/Person
• Implement the schema for Users/Person content types on the Event Platform
• Determine a consistent endpoint for serving that data to scrapers (with... security?)

Remaining tasks

User interface changes

API changes

Data model changes