Improve usability of external links

[xeniape]

Handling of external links

• Add an icon to indicate that one is leaving the Stackable documentation when clicking on it
• Open external links in a new tab

Is it possible/needed to write an AsciiDoc plugin or something similar to accomplish this?

PRs

• chore: improve usability of external links #778

[xeniape]

This can easily be accomplished by using {external-link-icon}^ in links, for example used here already: https://github.com/stackabletech/spark-k8s-operator/blob/7a8c2eee00275f3198d329f0bd0a6655cc0ad32a/docs/modules/spark-k8s/pages/index.adoc?plain=1#L16
This results in:

external-link-icon is defined in antora-playbook.yml of the documentation repo.