Add GitHub Issue templates for bug reports and feature requests

[omghante]

Problem

• Repo has no issue templates under .github/ISSUE_TEMPLATE/
• All issues are opened with a blank body
• Bug reports often lack SDK version, environment, and reproduction steps
• Feature requests lack structure around use cases and proposed solutions

Proposed Changes

• Add .github/ISSUE_TEMPLATE/bug_report.yml with fields for:
  • SDK version, Java version, environment, client type
  • Description, reproduction steps, expected and actual behavior
• Add .github/ISSUE_TEMPLATE/feature_request.yml with fields for:
  • Summary, use case, proposed solution, affected client
• Add .github/ISSUE_TEMPLATE/config.yml to:
  • Disable blank issues
  • Link to PhonePe developer docs