PR#527 and other editorial review corrections for Agama auto installation docs

[sounix000]

PR creator: Description

Corrections suggested by @dariavladykina in her PR #527, and some other corrections.
Starting this new PR because the original one containing Daria's corrections might have merge conflicts after large changes.

PR creator: Are there any relevant issues/feature requests?

• bsc#...
• jsc#...

PR reviewer: Checklist for editorial review

Apart from the usual checks, please double-check also the following:

• Cherry-picked to 16.0: c1f3ee2
• do any new files fulfill the naming conventions specified in https://github.com/SUSE/doc-modular/blob/main/templates/README.md?
• article title/structure title: does it have the required length and does it use sentence style capitalization?
• revhistory: is it up-to-date and does it follow the guidelines specified in https://documentation.suse.com/style/current/html/style-guide-db/sec-smartdocs.html#sec-revhistory?
• metadata: does it follow the guidlines specified in https://documentation.suse.com/style/current/html/style-guide-db/sec-smartdocs.html#sec-taglist-smartdocs?