Add subscript to issue templates

[opentelemetrybot]

If there are any issue templates, add a subscript to the very bottom of each one.

If there are no issue templates then DO NOTHING.

For markdown-based issue templates, use this subscript:

<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>

For yaml-based issue templates (aka issue forms), use this subscript:

  - type: dropdown
    attributes:
      label: Tip
      description: This element is static, used to render a helpful sub-heading for end-users and community members to help prioritize issues. Please leave as is.
      options:
        - <sub>[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>
      default: 0