Add duplicate-check to issue templates

Checklist

[x] I read and understood the Contributing Guidelines.
[x] This is not a duplicate of an existing merge request.
[x] I believe this falls into the scope of the project and should be part of the built-in functionality.
[x] My code follows the code style of this project.
[x] I have added tests to cover my changes, wherever they are necessary.
[x] All new and existing tests pass.

As per our conversation on ASF Discord server.