[interim fix] static files can't be delivered by HTTP.

Since PR 932 [1][2] static files can't be delivered by HTTP server any longer.

This patch makes the hash paramter in the URL of static files:

    /static/themes/simple/css/searxng.min.css?5fde34a74bc438c7b56ec8c6501e131cc9914bd8

optional.  By default the hash parameter is disabled.

HINT:

  Instances that do not deliver static files by their HTTP server and have a
  long expire time [3] should enable this option.

----

This is only a interim solution, on the long run:

    make static.build.commit

creates files including the file name:

    css/searxng-5fde34a74bc438c7b56ec8c6501e131cc9914bd8.min.css

and a mapping.json with this content[4]

[1] https://github.com/searxng/searxng/issues/964
[2] https://github.com/searxng/searxng/pull/932#issuecomment-1067039518
[3] 5583336440
[4] https://github.com/searxng/searxng/pull/932#issuecomment-1067216426

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

searx/settings_defaults.py

@@ -176,6 +176,7 @@ SCHEMA = {
     },
     'ui': {
         'static_path': SettingsDirectoryValue(str, os.path.join(searx_dir, 'static')),
+        'static_use_hash': SettingsValue(bool, False),
         'templates_path': SettingsDirectoryValue(str, os.path.join(searx_dir, 'templates')),
         'default_theme': SettingsValue(str, 'simple'),
         'default_locale': SettingsValue(str, ''),