* Move logic to determine noindex from view to model
This brings attention to the code and allows for faster unit tests.
I expect we'll be modifying this soon to deemphasize the code tag as a
marker of quality.
* Replace "5" constant with home feed minimum score
* Remove check for "code" tags in low quality article check
This made sense for DEV and other devrel communities, but is no longer
necessary for Forems.
* Add UserExperience setting for minimum index score
- add setting, I used `index_minimum_score` to match the
`home_feed_minimum_score`, `minimum_index_score` feels natural but
breaks the pattern.
- use this to determine whether to include article in the sitemap
- use this to determine whether to add noindex meta to article show page
* Remove unneeded tests
Since there's no longer any check for <code> tags in the body, omit
those tests (which passed anyway).
* Add new setting to admin page
