[mod] utils/searx.sh - add command 'inspect settings'

Inspect YAML setting <key> from SearXNG instance (${SEARX_SRC})::

  utils/searx.sh inspect settings server.base_url

utils/lib_install.sh
  should not log on stdout which is used for the output of function
  prompt_installation_setting().  Turned build_msg (stdout) into
  info_msg (stderr).

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