Modernize openvox-server install docs into structured section

[miharp]

Summary

• Replaces the single outdated install_from_packages page with a proper Installing and upgrading nav section, modeled on the openvox agent docs structure
• Adds three new pages: install_pre.md (before you begin), install_what_and_where.md (file layout), and upgrade_minor.md (upgrade procedure)
• Rewrites install_from_packages.markdown with current repo URLs, split apt/yum sections, and a verification step
• Updates _data/nav/openvox-server_8x.yml to replace the flat install link with a grouped section

Content changes

• Platform list updated from EOL versions to current supported OS/arch from yum.voxpupuli.org/openvox8 and apt.voxpupuli.org
• Java requirement corrected to 17 or 21 (verified from CI matrix in openvox-server repo)
• All puppet.com links replaced with openvox equivalents
• Removed outdated Java backports/universe repo workarounds

Closes #147

Test plan

• All four new/updated pages render correctly locally
• "Installing and upgrading" section appears in the openvox-server sidebar
• All nav links resolve to the correct pages
• No broken internal links
• All new files pass markdownlint

[miharp]

Validation notes

Supported OS and architecture

Platform and architecture support was verified directly from the package repository directory trees rather than from documentation:

• yum packages: browsed https://yum.voxpupuli.org/openvox8/ and crawled each OS family subdirectory (el/, amazon/, fedora/, sles/, redhatfips/) down to the architecture level to confirm which arches are published per version
• apt packages: checked https://apt.voxpupuli.org/ for supported Debian and Ubuntu codenames
• Java versions: verified from the CI matrix in the openvox-server repo (.github/workflows/pr-testing.yml), which tests against Java ['17', '21'] only — not 11 as the old page stated

What gets installed and where

Paths were verified against a running OpenVox Server (EL/aarch64) via Vagrant rather than inferred from documentation.

# Check binary and config paths directly
vagrant ssh puppet -c "ls /opt/puppetlabs/bin/puppetserver /opt/puppetlabs/bin/puppet /opt/puppetlabs/server/bin/ ..."

# Check log and runtime dirs with sudo
vagrant ssh puppet -c "sudo ls /etc/puppetlabs/puppetserver/conf.d/ /var/log/puppetlabs/puppetserver/ ..."

# Authoritative path lookup via puppet itself
vagrant ssh puppet -c "sudo /opt/puppetlabs/bin/puppet config print --section server"

Key findings that corrected the initial draft:

• /var/opt/puppetlabs/puppetserver/ does not exist — the server's vardir is /opt/puppetlabs/server/data/puppetserver/ (confirmed via puppet config print vardir --section server)
• CA material (ca_crt.pem, ca_crl.pem, signed certs, CSRs) lives at /etc/puppetlabs/puppetserver/ca/ (cadir), not in ssl/
• ssl/ (ssldir) holds only the server's own node certificate and private key
• /opt/puppetlabs/server/bin/ contains only puppetdb and puppetserver
• Three log files present: puppetserver.log, puppetserver-access.log, and puppetserver-status.log
• Migration backup path corrected to /etc/puppetlabs/ and /opt/puppetlabs/server/data/

[tuxmea]

All OpenVox related systems must ensure correct time setting.