Added Issues Templates acc. to industry standards

[naman9271]

Fixes: #1254

This pull request revamps the GitHub issue templates for the OpenML repository, replacing the old default template with a set of structured, user-friendly forms for bug reports, feature requests, documentation improvements, and security vulnerabilities. It also adds a configuration file to direct users to appropriate community resources and related repositories. These changes aim to improve issue triage, encourage responsible reporting, and make it easier for contributors to provide relevant information.

New Issue Templates and Configuration

• Added dedicated YAML-based templates for bug reports (bug_report.yml), feature requests (feature_request.yml), documentation improvements (documentation.yml), and security vulnerability reports (security.yml). Each template includes clear instructions, required fields, and checklists to guide users in submitting actionable issues.
• Removed the old markdown-based default issue template (default-issue-template.md), consolidating all issue types under the new structured forms.

Repository and Community Guidance

• Added a .github/ISSUE_TEMPLATE/config.yml file to enable blank issues and provide contact links for community discussions, documentation, website, and API-specific issue trackers. This helps users find the right place for their questions and reports.

[naman9271]

Hi @joaquinvanschoren , @janvanrijn please review when you get a chance - thanks