Improve Telegram message deduplication

* Add pre-send message database check for deduplication
* Make dedup cache queue length configurable

example-config.yaml

@@ -136,6 +136,16 @@ bridge:
     # your own Matrix account as the Matrix puppet for your Telegram account.
     sync_with_custom_puppets: true
 
+    # Some config options related to Telegram message deduplication.
+    # The default values are usually fine, but some debug messages/warnings might recommend you
+    # change these.
+    deduplication:
+        # Whether or not to check the database if the message about to be sent is a duplicate.
+        pre_db_check: false
+        # The number of latest events to keep when checking for duplicates.
+        # You might need to increase this on high-traffic bridge instances.
+        cache_queue_length: 20
+
     # The formats to use when sending messages to Telegram via the relay bot.
     #
     # Telegram doesn't have built-in emotes, so the m.emote format is also used for non-relaybot users.