Simplify GitHub issue templates

[eddybrando]

Feature description

We currently have multiple templates for GitHub issues:

• Bug report (Content)
• Bug report (Other)
• Feature request
• Provide update
• User research
• User story
• Report a security vulnerability
• Qiskit Textbook issues

We should update this list since we no longer need to support such complexity in this repository.

Probably just having the 2 default templates "Bug report" and "Feature request" might be enough for this project now.

Additional context

No response