Based on GitHub documentation I can create a custom Bug Report template, and in that i can customize the Markup that fits the business need.
OOTB bug and custom templates have same fields (Assignees, Projects, Labels, Milestones... etc) But how can I add custom fields to it (For e.g. Priority, Severity, Planning Status etc...)
Another example is AzureDevOps allows definition of custom templates and custom fields for bugs or feature enhancements.
Can I achieve similar in GitHub templates ?
Apr. 2020: From the documentation, there do not seem to be any option to add custom fields.
That maybe because of the management involved with any new field: for instance, limiting the values of "Priority" to only a fixed set (like "low", "medium" and "high")
Since each custom field would require its own set of rules and validation, this is not currently available for GitHub issue template.
Update June 2021:
New beta features within GitHub Issues, with better ways to plan, track, and manage projects.
Read more on the GitHub Issues page or in the FAQ.
✨ NEW – Project planning for developersAvailable in limited public beta
Built like a spreadsheet, project tables give you a live canvas to filter, sort, and group issues and pull requests.
Tailor them to your needs with custom fields and saved views.