Link to new issue with a preselected template

Description

Templates in new issues are a useful tool to pre-fill information as part of a workflow. This requires a manual action, and unfortunately this is a bit tedious when an external application (or a README or something) points to a GitLab project's New Issue page from a link un a context that knows which kind of template should be set.

Proposal

Allow the URL to contain the template to be set, so as to reach the New Issue page with a pre-selected template and pre-filled issue with the provided template.