STYLE: Improve the first interaction message style

Improve the first interaction message style:
- Remove the section header markup (`#`) and avoid an excessively large
  font/avoid making the interaction message prevail over the issue/PR
  text itself.
- Use the YAML literal block style syntax (`|`) and remove the newline
  explicit markup.

Author: jhlegarreta

.github/workflows/first-interaction.yml

@@ -15,5 +15,17 @@ jobs:
     - uses: actions/first-interaction@v1
       with:
         repo-token: "${{ secrets.GITHUB_TOKEN }}"
-        issue-message: '# Thank you for contributing an issue\n**Welcome to the ITK community!**\nWe are glad you are here and appreciate your contribution. Please keep in mind our [community participation guidelines](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CODE_OF_CONDUCT.md).\nAlso, please check [existing open issues](https://github.com/InsightSoftwareConsortium/ITK/issues) and consider discussion on the [ITK Discourse](https://discourse.itk.org).'
-        pr-message: '# Thank you for contributing a pull request\n**Welcome to the ITK community!**\nWe are glad you are here and appreciate your contribution. Please keep in mind our [community participation guidelines](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CODE_OF_CONDUCT.md).\nMore support and guidance on the contribution process and be found in our [contributing guide](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CONTRIBUTING.md).'
+        issue-message: |
+          Thank you for contributing an issue!
+
+          **Welcome to the ITK community!**
+
+          We are glad you are here and appreciate your contribution. Please keep in mind our [community participation guidelines](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CODE_OF_CONDUCT.md).
+          Also, please check [existing open issues](https://github.com/InsightSoftwareConsortium/ITK/issues) and consider discussion on the [ITK Discourse](https://discourse.itk.org).
+        pr-message: |
+          Thank you for contributing a pull request!
+
+          **Welcome to the ITK community!**
+
+          We are glad you are here and appreciate your contribution. Please keep in mind our [community participation guidelines](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CODE_OF_CONDUCT.md).
+          More support and guidance on the contribution process and be found in our [contributing guide](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CONTRIBUTING.md).