Add more configuration options and allow setting per-URL config via tags like `depth=1`

Ideally, the options provided on the add page should also be present in the extension configuration (e.g. crawl depth and extractor methods).

In the future, it would also be nice to have this be able to be set per-domain.

Start by reviewing the options exposed on the add page and the current extension configuration. Define how crawl depth and extractor methods should be configured, then determine the scope and behavior for per-URL tags such as `depth=1` and future per-domain settings; done should include documented behavior and coverage for the agreed options.

Written by the indexing model from the issue text.