[FEATURE] optional special handling of external links

David-Guillot commented 1 month ago

What does this PR change? What problem does it solve?

This PR proposes a way to optionally open external links to a new tab, and optionally mark external links with an icon.

Was the change discussed in an issue or in the Discussions before?

Closes #1612.

PR Checklist

[ ] This change adds/updates translations and I have used the template present here.
[x] I have enabled maintainer edits for this PR.
[x] I have verified that the code works as described/as intended.
[ ] This change adds a Social Icon which has a permissive license to use it.
[x] This change does not include any CDN resources/links.
[x] This change does not include any unrelated scripts such as bash and python scripts.
[x] This change updates the overridden internal templates from HUGO's repository.