Add GitHub issue templates with YAML forms

[Copilot]

Implements structured YAML-based issue templates to enforce consistent bug reports and feature requests, with blank issues disabled.

Changes

• .github/ISSUE_TEMPLATE/config.yml - Disables blank issues, adds contact links for Discussions and Security Advisories
• .github/ISSUE_TEMPLATE/bug_report.yml - Bug report form with required fields (description, expected/actual behavior, repro steps), version dropdowns (.NET, OS), and C# code sample support
• .github/ISSUE_TEMPLATE/feature_request.yml - Feature request form with required fields (summary, problem, solution, use case), categorization dropdowns, and contribution intent selector

All templates use GitHub's form schema with validation to ensure complete submissions.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Issue templates should be created</issue_title>
<issue_description>Issue templates should be created for bug reports and feature requests.

These should be structured YAML based forms to validate the submissions.

The templates should be configured to disable blank issues and enforce template usage, and appropriate contact links placed for discussions and security advisories.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Issue templates should be created #80

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