PyGithub
Add IssueType support to create/edit issues
Describe the problem the Pull Request attempts to solve
When creating issues, I want to be able to set the type of the issue. I may also want to edit the type of an existing issue.
Explain how the you went about solving the problem
Added the relevant params to the create issue func and edit issue func.
Provide a test that exemplifies the expected behaviour
TODO
One thing i should mention incase someone is wondering, I used the param name issue_type rather than type as that is a builtin. It looks like in https://github.com/PyGithub/PyGithub/pull/3381 @nrysk set the param name to type, which conflicts with the builtin type() function. I am more than happy to change the param type to issue_type in this pr, unless you guys would prefer a separate pr?
