Add a REST API interface to engage with the crawl engine

[anjackson]

Should we add a FastAPI module so the crawler can have a REST API for launching a crawl. Possibly also for managing scope and seeds files? This could also expose crawl stats etc. The overall approach would be to avoid forcing services that interact with the crawler having to go through Kafka, at least for crawl launches.

This could be made consistent with the Browsertrix-Crawler API/model, so we essentially have two separate crawl engines that we can interact with in consistent ways.