[DOC] remove technical preview from Running Logstash on K8s page

[kaisecheng]

fix: #17045

[github-actions]

📃 DOCS PREVIEW ✨ https://logstash_bk_17175.docs-preview.app.elstc.co/diff

[mergify]

This pull request does not have a backport label. Could you fix it @kaisecheng? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label.