Enhance issue & pull request templates

Currently:
- issue & pull request templates are only available on some docling-project repos
- the bug issue template is only hinting at input files needed for reproducing bugs — but those are actually very often necessary but missing, which leads to increased communication effort and resolution time

Enhance the templates by:
- [ ] creating centralized defaults over at https://github.com/docling-project/.github (can be based on [docling templates](https://github.com/docling-project/docling/tree/main/.github))
- [ ] adding an explicit checkbox in the bug template, along the lines of "I am attaching any input file needed for reproducing this (provided I'm allowed to), otherwise I acknowledge the issue may not be reproducible."
- [ ] leveraging the `type` (until now we have only be setting the `labels`)
- [ ] adding a performance issue template: similar to bug, but using the `performance` label instead
- [ ] [advanced] experimenting with providing issue templates via the recently introduced issue forms

Reference:
https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/configuring-issue-templates-for-your-repository