Expand non-quick installation content

[tahliar]

PR creator: Description

Adding a full deployment guide Expanding the Admin Guide installation content so that all the options are clear. This does not replace the Installation and Setup Quick Start, which has a different use case.

This is an expansion of the installation content for 15 SP7. It can be fine-tuned even further (and crossover with SAP more) in SLE 16, which has a whole new structure that makes sharing content easier.

Here's a PDF of the Admin Guide as a whole:
book-administration_en.pdf
For the most part I made changes to Part I: Installation and setup, but I did make a few changes in other parts too. I'll add a section below that goes into greater detail about the changes, since the diff is too big to be coherent.
See Summary of changes below.

This was a long-term project and therefore needed to be rebased regularly, so the commit dates in this PR do not reflect reality.

I originally kept track of the relevant product changes for each SP, but I've decided that it doesn't make sense to backport this, both because of complexity and to avoid issues with the localised content in earlier versions.

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

• jsc#PED-2842

PR creator: Which product versions do the changes apply to?

When opening a PR, check all versions of the documentation that your PR applies to.

• SLE-HA 15
  • 15 next (current main, no backport necessary)
  • 15 SP6
  • 15 SP5
  • 15 SP4
  • 15 SP3
  • 15 SP2
• SLE-HA 12
  • 12 SP5

PR reviewer only: Have all backports been applied?

The doc team member merging your PR will take care of backporting to older documents.
When opening a PR, do not set the following check box.

• all necessary backports are done

Summary of changes

Main change: major expansion of the content in "Part I: Installation and setup"

For this I'll attach a PDF, as it's a whole Part. This PDF contains only Part I:
part-install_en.pdf

New content

• Added a new chapter "2 Installation overview". This gives an introduction to the rest of the chapters in this part, i.e. the high-level procedure for setting up a cluster.
• Added a new chapter "4 Logging in to the cluster nodes". Before installing anything, this explains the root vs sudo user options, and SSH agent forwarding.
• Added a new chapter "6 Using the bootstrap scripts". This goes into detail about crm cluster init and crm cluster join, with options beyond just the quickstart defaults. It also includes a quick section on crm cluster remove.
• Added a new section "7.4 Configuring an arbitrator for quorum decisions" because the QDevice window in YaST wasn't documented before.

Edited content

• Slightly restructured chapter "1 Product overview", including making STONITH stand out more in section "1.4 Architecture".
• Slightly restructured chapter "7 Using the YaST cluster module" to follow the initial wizard better, but moved the non-YaST parts to the end (i.e. transferring the config to all nodes and starting the cluster).
• Tested and updated all sections in chapter "7 Using the YaST cluster module".
• Moved AutoYaST to a separate chapter "8 Deploying nodes with AutoYaST".

Minor change: Updated/edited sections of "Part II: Configuration and administration"

This is new content to explain more of the post-installation functions of crm cluster init that weren't already documented.

Note that the syntax highlighting in the HTML render is a bit odd right now, but that's a style sheet issue.

• In section "9.5.1 User privileges and authentication":

• In section "9.5.11 Managing Corosync configuration":