[MM-47896] Channel names can collide with GM names (#21639)

* Block channel creation if name matches GM naming pattern

* Fix regex and error text

* Add test for DM names

* Update error string

* Trigger build

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

i18n/en.json

@@ -8121,7 +8121,7 @@
   },
   {
     "id": "model.channel.is_valid.name.app_error",
-    "translation": "Invalid channel name. User ids are not permitted in channel name for non-direct message channels."
+    "translation": "Channel names can't be in a hexadecimal format. Please enter a different channel name."
   },
   {
     "id": "model.channel.is_valid.purpose.app_error",