docs: enrich issue template chooser with contact links

[hasansezertasan]

Context

The current .github/ISSUE_TEMPLATE/config.yaml only contains blank_issues_enabled: false. PR #16 enriched it with contact_links (docs, website, Discord) to route people to the right place before opening an issue.

⚠️ Note on PR #16's version

PR #16 wrote blank_lines_enabled: true — this key is invalid. GitHub only recognizes blank_issues_enabled, so that line is silently ignored (and defaults blank issues back to enabled). We should:

• Keep the correct key blank_issues_enabled (proposal: keep false to preserve current behavior)
• Add the contact_links block
• Use the modern discord.gg/litestar invite

Proposed tasks

• Add contact_links (Litestar Documentation, Litestar Website, Discord) to config.yaml
• Preserve blank_issues_enabled: false
• (Optional follow-up) update the stale discord.gg/MmcwxztmQb invite in pyproject.toml