Add workflow create_dispatch method that raises exceptions

[dblanchette]

(Reopen broken #2965)

We've been having issues with creating workflow dispatch with missing/too many arguments.

When using Workflow.create_dispatch(), we only get a boolean response even though the GitHub API returns detailed error messages.

This creates a new method that returns an exception with the error data when it fails. I did that not to break the existing method.

[EnricoMi]

See #2760 as the general design issue.

[EnricoMi]

Maybe we should add attribute throw: bool = False to create_dispatch, which when False exhibits the current (flawed) behaviour (return status == 204), and when set True calls into requestJsonAndCheck, which will raise errors when status is not 2xx.

In v3, throw will be set to True as the default (breaking change) and will eventually be removed.