Improve docs

[jwag956]

Made a sweep through all the docs and fixed/improved things:

• added missing recoverY_codes API
• added missing change_email signals
• many openapi requests had a missing 'type: string' so didn't render
• added sphinx extension autosectionlabel to make it easier to link
• moved overview and search to top of doc pages (for some long pages like API - it was hard to find them at the bottom).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.44%. Comparing base (442faf3) to head (ff98e12).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #977 +/- ## ======================================= Coverage 98.44% 98.44% ======================================= Files 36 36 Lines 4625 4625 ======================================= Hits 4553 4553 Misses 72 72 ```

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