MM-21357: Use typed constant for channel types (#17928)

* MM-21357: Use typed constant for channel types

https://mattermost.atlassian.net/browse/MM-21357

```release-note
- Introduced a new type ChannelType for all channel types.
- Updated the Client4.UpdateChannelPrivacy method to ChannelType.
```

* Address review comments

```release-note
NONE
```

* telemetry fix

```release-note
NONE
```

services/telemetry/telemetry_test.go

@@ -101,9 +101,9 @@ func initializeMocks(cfg *model.Config) (*mocks.ServerIface, *storeMocks.Store,
 	teamStore.On("GroupSyncedTeamCount").Return(int64(16), nil)
 
 	channelStore := storeMocks.ChannelStore{}
-	channelStore.On("AnalyticsTypeCount", "", "O").Return(int64(25), nil)
-	channelStore.On("AnalyticsTypeCount", "", "P").Return(int64(26), nil)
-	channelStore.On("AnalyticsTypeCount", "", "D").Return(int64(27), nil)
+	channelStore.On("AnalyticsTypeCount", "", model.ChannelTypeOpen).Return(int64(25), nil)
+	channelStore.On("AnalyticsTypeCount", "", model.ChannelTypePrivate).Return(int64(26), nil)
+	channelStore.On("AnalyticsTypeCount", "", model.ChannelTypeDirect).Return(int64(27), nil)
 	channelStore.On("AnalyticsDeletedTypeCount", "", "O").Return(int64(22), nil)
 	channelStore.On("AnalyticsDeletedTypeCount", "", "P").Return(int64(23), nil)
 	channelStore.On("GroupSyncedChannelCount").Return(int64(17), nil)