Add ignore_prefix config option

When reply_without_command is enabled, a message starting with this character (or string) will not be sent as a reply

bot.py

@@ -1197,7 +1197,7 @@ async def on_message(self, message):
 
         await self.process_commands(message)
 
-    async def process_commands(self, message):
+    async def process_commands(self, message: discord.Message):
         if message.author.bot:
             return
 
@@ -1231,7 +1231,8 @@ async def process_commands(self, message):
                     or self.config.get("anon_reply_without_command")
                     or self.config.get("plain_reply_without_command")
                 ):
-                    await thread.reply(message, anonymous=anonymous, plain=plain)
+                    if not message.content.startswith(self.config.get("ignore_prefix")):
+                        await thread.reply(message, anonymous=anonymous, plain=plain)
                 else:
                     await self.api.append_log(message, type_="internal")
             elif ctx.invoked_with:

core/config.py

@@ -39,6 +39,7 @@ class ConfigManager:
         "reply_without_command": False,
         "anon_reply_without_command": False,
         "plain_reply_without_command": False,
+        "ignore_prefix": "\0",
         # logging
         "log_channel_id": None,
         "mention_channel_id": None,

core/config_help.json

@@ -195,6 +195,16 @@
             "See also: `anon_reply_without_command`, `plain_reply_without_command`."
         ]
     },
+    "ignore_prefix": {
+        "default": "\\0",
+        "description": "Messages that start with this prefix will be ignored by Modmail.",
+        "examples": [
+            "`{prefix}config set ignore_prefix .`"
+        ],
+        "notes": [
+            "`reply_without_command` must be enabled"
+        ]
+    },
     "anon_reply_without_command": {
         "default": "Disabled",
         "description": "Setting this configuration will make all non-command messages sent in the thread channel to be anonymously forwarded to the recipient without the need of `{prefix}reply`.",