Added module for filtering transcription requests from presence stanz… (#6404)

* Added module for filtering transcription requests from presence stanzas when the users making the requests do not have access to the transcription feature

* Add comments explaining the functionality and configuration for the transcription filtering module.

Co-authored-by: drimovecz <daniel.rimovecz@8x8.com>

resources/prosody-plugins/mod_muc_transcription_filter.lua

+--This module performs features checking when a transcription is requested.
+--If the transcription feature is not allowed, the tag indicating that a
+--transcription is being requested will be stripped from the presence stanza.
+--The module must be enabled under the muc component.
+local is_feature_allowed = module:require "util".is_feature_allowed;
+
+module:log("info", "Loading mod_muc_transcription_filter!");
+local filtered_tag_name = "jitsi_participant_requestingTranscription";
+
+function filter_transcription_tag(event)
+    local stanza = event.stanza;
+    local session = event.origin;
+    if stanza and stanza.name == "presence" then
+        if not is_feature_allowed(session,'transcription') then
+            stanza:maptags(function(tag)
+                if tag and tag.name == filtered_tag_name then
+                    module:log("info", "Removing %s tag from presence stanza!", filtered_tag_name);
+                    return nil;
+                else
+                    return tag;
+                end
+            end)
+        end
+    end
+end
+
+module:hook("presence/bare", filter_transcription_tag);
+module:hook("presence/full", filter_transcription_tag);
+module:hook("presence/host", filter_transcription_tag);
+
+module:log("info", "Loaded mod_muc_transcription_filter!");