Add support for title parameter in conversations.canvases.create method

### Description
[conversations.canvases.create](https://docs.slack.dev/reference/methods/conversations.canvases.create/) method now supports passing `title` argument. Add support for the argument to the `CreateChannelCanvas` method.

### (Optional) Slack's documentation
https://docs.slack.dev/reference/methods/conversations.canvases.create/