[FEAT] - Create App Search Engine if it doesn't exist on crawl

[wambozi]

Is your feature request related to a problem? Please describe.

Currently, if an engine doesn't exist in App Search when a crawl of that type is started, the crawler throws 404s in the logs. It would be better if the webcrawler detected if the engine was there, and if not create it, before continuing with the crawl.

Describe the solution you'd like

A POST like:

curl -XPOST http://localhost:8081/crawl -d {
    "engine": "demo",
    "url": "http://www.example.com",
    "type": "app-search"
}

Will detect if the engine specified exists, and if not create it.