chore: use rendered issue templates

[zimeg]

Changelog

No user-facing changes.

Summary

Updates issue templates to use GitHub's rendered issue form format with structured fields and validation.

• Replaces markdown (.md) issue templates with YAML (.yml) issue forms
• Adds config.yml to disable blank issues and link to Slack customer support
• Removes the generic issue_template.md (superseded by specific templates)

Preview

👁️‍🗨️ https://github.com/slackapi/slack-cli/issues/new/choose

References

📚 https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/configuring-issue-templates-for-your-repository
🔗 slackapi/node-slack-sdk#2518

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.21%. Comparing base (346be01) to head (7b4ac54).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #488   +/-   ##
=======================================
  Coverage   71.21%   71.21%           
=======================================
  Files         222      222           
  Lines       18664    18664           
=======================================
  Hits        13292    13292           
  Misses       4190     4190           
  Partials     1182     1182           

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[zimeg]

A note for the reviewer 🧮

[zimeg]

🔍 note: The order of issue templates was adjusted to be:

1. Question
2. Bug
3. Feature request
4. Documentation