MM-53687: Block changes to name, display name or purpose for direct and group messages (#24199)

* block changes to name, display name or purpose for direct and group messages

* add test

* fix condition

* update patch_channel

* update error message

* fix message

* fix lint

* fix i18n

```release-note
NONE
```

---------

Co-authored-by: Agniva De Sarker <agnivade@yahoo.co.in>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/channel.go

@@ -170,6 +170,10 @@ func updateChannel(c *Context, w http.ResponseWriter, r *http.Request) {
 			c.Err = model.NewAppError("updateChannel", "api.channel.patch_update_channel.forbidden.app_error", nil, "", http.StatusForbidden)
 			return
 		}
+		if (channel.Name != "" && channel.Name != oldChannel.Name) || (channel.DisplayName != "" && channel.DisplayName != oldChannel.DisplayName) || (channel.Purpose != oldChannel.Purpose) {
+			c.Err = model.NewAppError("updateChannel", "api.channel.update_channel.update_direct_or_group_messages_not_allowed.app_error", nil, "", http.StatusBadRequest)
+			return
+		}
 
 	default:
 		c.Err = model.NewAppError("updateChannel", "api.channel.patch_update_channel.forbidden.app_error", nil, "", http.StatusForbidden)
@@ -342,6 +346,10 @@ func patchChannel(c *Context, w http.ResponseWriter, r *http.Request) {
 			c.Err = model.NewAppError("patchChannel", "api.channel.patch_update_channel.forbidden.app_error", nil, "", http.StatusForbidden)
 			return
 		}
+		if (patch.Name != nil && *patch.Name != oldChannel.Name) || (patch.DisplayName != nil && *patch.DisplayName != oldChannel.DisplayName) || (patch.Purpose != nil && *patch.Purpose != oldChannel.Purpose) {
+			c.Err = model.NewAppError("patchChannel", "api.channel.patch_update_channel.update_direct_or_group_messages_not_allowed.app_error", nil, "", http.StatusBadRequest)
+			return
+		}
 
 	default:
 		c.Err = model.NewAppError("patchChannel", "api.channel.patch_update_channel.forbidden.app_error", nil, "", http.StatusForbidden)