[enh] add woxikon.de synonyme (Xpath)

Added synonyme.woxikon.de using the xpath engine.  Adds a site which returns
word synonyms although just in German.

Depending on the query not all synonyms are shown because of not the best xpath
selection.  But should do the job just fine.

Upstream example query: https://synonyme.woxikon.de/synonyme/test.php

searx/settings.yml

@@ -1477,6 +1477,23 @@ engines:
     timeout: 5.0
     disabled: true
 
+  - name: woxikon.de synonyme
+    engine: xpath
+    shortcut: woxi
+    categories: general
+    timeout: 5.0
+    disabled: true
+    search_url: https://synonyme.woxikon.de/synonyme/{query}.php
+    url_xpath: //div[@class="upper-synonyms"]/a/@href
+    content_xpath: //div[@class="synonyms-list-group"]
+    title_xpath: //div[@class="upper-synonyms"]/a
+    about:
+      website: https://www.woxikon.de/
+      wikidata_id: # No Wikidata ID
+      use_official_api: false
+      require_api_key: false
+      results: HTML
+
   - name: słownik języka polskiego
     engine: sjp
     shortcut: sjp