[fix] make autofocus configurable (#1984) (#3285)

* [fix] make autofocus configurable (#1984)

"Results page: having text cursor still in search field is annoying #1984"

Allows autofocus on the results page to be configured either in the UI
or in the searx server config.

* fix commented code

Co-authored-by: Ben Collerson <benc@benon.com>