Add Create/Get/Delete for oauth2 apps
Add Create, List, and Delete for Oauth2 applications.
Tests were added as well.
Co-authored-by: Dan Molik <dan@danmolik.com>
Reviewed-on: https://gitea.com/gitea/go-sdk/pulls/305
Reviewed-by: techknowlogick <techknowlogick@gitea.io>
Reviewed-by: 6543 <6543@noreply.gitea.io>
