[Docs] Update community plugins documentation (elastic#197569)

This PR recreates [@aakash742's
PR](elastic#196497) to add a note about
Elastic not providing support for community plugins

---------

Co-authored-by: akashsingh <55509676+aakash742@users.noreply.github.com>
(cherry picked from commit 762903e)

docs/user/plugins.asciidoc

@@ -18,7 +18,8 @@ Plugin developers must release a new version of their plugin for each new {kib}
 == Known plugins
 
 The known plugins were tested for {kib} *5.x*, so we are unable to guarantee compatibility with your version of {kib}. The {kib} installer rejects any plugins that haven't been published for your specific version of {kib}. 
-We are unable to evaluate or maintain the known plugins, so care should be taken before installation.
+
+IMPORTANT: Known plugins are developed and maintained outside of Elastic. They are not supported by Elastic. If you encounter an issue with a community plugin, contact the plugin's owner.
 
 [float]
 === Apps
@@ -182,4 +183,4 @@ you must specify the path to that configuration file each time you use the `bin/
 0:: Success
 64:: Unknown command or incorrect option parameter
 74:: I/O error
-70:: Other error
+70:: Other error