Restore AIX packages and purge Alpine references

[vikman90]

Description

This PR aims to apply two changes:

1. Restore back the AIX@PPC package reference as we removed it by mistake.
2. Remove all references to the agent installation/upgrade on Alpine Linux, as it's no longer supported.

Checks

Docs building

• Compiles without warnings.

Code formatting and web optimization

• Uses three spaces indentation.
• Adds or updates meta descriptions accordingly.
• Updates the redirects.js script if necessary (check this guide).

Writing style

• Uses present tense, active voice, and semi-formal registry.
• Uses short, simple sentences.
• Uses bold for user interface elements, italics for key terms or emphasis, and code font for Bash commands, file names, REST paths, and code.

[javimed]

If not Alpine, what systems? Too vague. We should clarify or remove altogether.