fix: Use internal_hashed everywhere. (#8485)

doc/debian/jitsi-meet-prosody/prosody.cfg.lua-jvb.example

     muc_room_default_public_jids = true
 
 VirtualHost "auth.jitmeet.example.com"
-    authentication = "internal_plain"
+    authentication = "internal_hashed"
 
 -- Proxy to jicofo's user JID, so that it doesn't have to register as a component.
 Component "focus.jitmeet.example.com" "client_proxy"

doc/example-config-files/multidomain/prosody.cfg.multidomain.example

 -- server please see http://prosody.im/doc/modules/mod_auth_internal_hashed
 -- for information about using the hashed backend.
 
 authentication = "internal_hashed"
 
 -- Select the storage backend to use. By default Prosody uses flat files
         key = "/var/lib/prosody/auth.jitsi.example.com.key";
         certificate = "/var/lib/prosody/auth.jitsi.example.com.crt";
     }
-    authentication = "internal_plain"
+    authentication = "internal_hashed"
 
 ------ Components ------
 -- You can specify components to add hosts that provide special services,

doc/example-config-files/prosody.cfg.lua.example

 -- server please see http://prosody.im/doc/modules/mod_auth_internal_hashed
 -- for information about using the hashed backend.
 
 authentication = "internal_hashed"
 
 -- Select the storage backend to use. By default Prosody uses flat files
         key = "/var/lib/prosody/auth.jitsi.example.com.key";
         certificate = "/var/lib/prosody/auth.jitsi.example.com.crt";
     }
-    authentication = "internal_plain"
+    authentication = "internal_hashed"
 
 ------ Components ------
 -- You can specify components to add hosts that provide special services,

doc/example-config-files/scalable/meet.example.com.cfg.lua.scalable.example

         key = "/etc/prosody/certs/auth.meet.example.com.key";
         certificate = "/etc/prosody/certs/auth.meet.example.com.crt";
     }
-    authentication = "internal_plain"
+    authentication = "internal_hashed"
 
 Component "focus.meet.example.com"
     component_secret = "jicofo_secret_test"
     modules_enabled = {
         "ping";
     }
-    authentication = "internal_plain"
+    authentication = "internal_hashed"
     c2s_require_encryption = false