In PR-2894[1] we isolated botdetection from the limiter, this PR isolates the
botdetection from the SearXNG core code.
This PR also fixes the issue [2] that the ``server.public_instance`` option
needs to activate the limiter.
- [1] https://github.com/searxng/searxng/pull/2894
- [2] https://github.com/searxng/searxng/issues/2975
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
