feat: provide submit options for `mr create` and `issue create`
Provide submit options to allow users either submit the MR via the CLI or continue in browser or cancel.
If 'preview in browser' is selected, it opens up a browser window with a prefilled title, description and other mr or issue options.
Note on Prefilling issue with url query parameters: gitlab-foss#19731 (comment 32449479) and slash commands: gitlab-foss#19731 (comment 32550046)
Resolves #329 (closed)