[doc] rearranges Settings & Engines docs for better readability

We have built up detailed documentation of the *settings* and the *engines* over
the past few years.  However, this documentation was still spread over various
chapters and was difficult to navigate in its entirety.

This patch rearranges the Settings & Engines documentation for better
readability.

To review new ordered docs::

   make docs.clean docs.live

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/admin/settings/settings_search.rst

@@ -0,0 +1,97 @@
+.. _settings search:
+
+===========
+``search:``
+===========
+
+.. code:: yaml
+
+   search:
+     safe_search: 0
+     autocomplete: ""
+     default_lang: ""
+     ban_time_on_fail: 5
+     max_ban_time_on_fail: 120
+     suspended_times:
+       SearxEngineAccessDenied: 86400
+       SearxEngineCaptcha: 86400
+       SearxEngineTooManyRequests: 3600
+       cf_SearxEngineCaptcha: 1296000
+       cf_SearxEngineAccessDenied: 86400
+       recaptcha_SearxEngineCaptcha: 604800
+     formats:
+       - html
+
+``safe_search``:
+  Filter results.
+
+  - ``0``: None
+  - ``1``: Moderate
+  - ``2``: Strict
+
+``autocomplete``:
+  Existing autocomplete backends, leave blank to turn it off.
+
+  - ``dbpedia``
+  - ``duckduckgo``
+  - ``google``
+  - ``startpage``
+  - ``swisscows``
+  - ``qwant``
+  - ``wikipedia``
+
+``default_lang``:
+  Default search language - leave blank to detect from browser information or
+  use codes from :origin:`searx/languages.py`.
+
+``languages``:
+  List of available languages - leave unset to use all codes from
+  :origin:`searx/languages.py`.  Otherwise list codes of available languages.
+  The ``all`` value is shown as the ``Default language`` in the user interface
+  (in most cases, it is meant to send the query without a language parameter ;
+  in some cases, it means the English language) Example:
+
+  .. code:: yaml
+
+     languages:
+       - all
+       - en
+       - en-US
+       - de
+       - it-IT
+       - fr
+       - fr-BE
+
+``ban_time_on_fail``:
+  Ban time in seconds after engine errors.
+
+``max_ban_time_on_fail``:
+  Max ban time in seconds after engine errors.
+
+``suspended_times``:
+  Engine suspension time after error (in seconds; set to 0 to disable)
+
+  ``SearxEngineAccessDenied``: 86400
+    For error "Access denied" and "HTTP error [402, 403]"
+
+  ``SearxEngineCaptcha``: 86400
+    For error "CAPTCHA"
+
+  ``SearxEngineTooManyRequests``: 3600
+    For error "Too many request" and "HTTP error 429"
+
+  Cloudflare CAPTCHA:
+     - ``cf_SearxEngineCaptcha``: 1296000
+     - ``cf_SearxEngineAccessDenied``: 86400
+
+  Google CAPTCHA:
+    - ``recaptcha_SearxEngineCaptcha``: 604800
+
+``formats``:
+  Result formats available from web, remove format to deny access (use lower
+  case).
+
+  - ``html``
+  - ``csv``
+  - ``json``
+  - ``rss``