Implementing Phoenix-side code to crawl documents using OTA engine

[madoleary]

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This PR would implement the OTA engine for crawling document text on document creation, update, and for individual crawls made on-demand by the user. This addresses issue https://github.com/tosdr/edit.tosdr.org/issues/1168

It also includes error-handling and removes references to the old crawler system.

[michielbdejong]

Code is working in development but merging this PR to main is still blocked on https://github.com/tosdr/edit.tosdr.org/issues/1186 since (we think) that would trigger a deploy to production - don't merge this PR until the necessary production environment variables are in place!

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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0.0% Coverage on New Code
0.0% Duplication on New Code

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