Add a feature-request issue template

[hanneshapke]

.github/ISSUE_TEMPLATE/ only contains a bug-report template (10_bug_report.yml) and config.yml. Feature requests currently land as free-form issues with inconsistent structure.

What to add

Create .github/ISSUE_TEMPLATE/20_feature_request.yml (matching the schema/style of the existing bug-report template) with fields:

• Problem / motivation
• Proposed solution
• Alternatives considered
• Additional context / use case

Hints

• Use the same YAML form schema as 10_bug_report.yml.
• Reference GitHub's issue forms docs.

Difficulty: good first issue, ~30 min.