Add text/markdown to Tika mime-type database

Done upstream in apache/tika#2806

Fixes: QTBUG-146675
Change-Id: I5c13064228da4355d4b3c132d3242cd612f0aa0a
Pick-to: 6.10 6.8
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Dennis Oberst <dennis.oberst@qt.io>
(cherry picked from commit 10e1b1f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

Author: ec1oud

src/corelib/mimetypes/3rdparty/tika-mimetypes.xml

@@ -8147,8 +8147,10 @@
     <sub-class-of type="text/plain"/>
   </mime-type>
 
-  <mime-type type="text/x-web-markdown">
-    <comment>Markdown source code</comment>
+  <mime-type type="text/markdown">
+    <comment>Markdown document</comment>
+    <alias type="text/x-web-markdown"/>
+    <alias type="text/x-markdown"/>
     <glob pattern="*.md"/>
     <glob pattern="*.mdtext"/>
     <glob pattern="*.mkd"/>