Add subscript to issue templates

[Copilot]

This PR adds a subscript to all issue templates to help users prioritize issues with reactions and provide meaningful context instead of simple +1 comments.

Changes Made

Added the following subscript to the bottom of all 5 markdown-based issue templates:

<sub>**Tip**: [React](https://github.blog/news-insights/product-news/add-reactions-to-pull-requests-issues-and-comments/) with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding `+1` or `me too`, to help us triage it. Learn more [here](https://opentelemetry.io/community/end-user/issue-participation/).</sub>

Files Modified

• .github/ISSUE_TEMPLATE/bug_report.md
• .github/ISSUE_TEMPLATE/discussion.md
• .github/ISSUE_TEMPLATE/feature_request.md
• .github/ISSUE_TEMPLATE/instrumentation_request.md
• .github/ISSUE_TEMPLATE/ownership_request.md

Impact

This change will help:

• Guide users to use GitHub reactions (👍) to help prioritize issues
• Encourage meaningful comments instead of simple "+1" or "me too" responses
• Provide a link to community participation guidelines
• Improve issue triage efficiency for maintainers

The changes are minimal and preserve all existing template content, only adding the helpful subscript at the bottom of each template.

Fixes #26.

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