docs: fix SELinux policy guidance and add CentOS EOL notices to LAMP/LEMP guides

[somethingwithproof]

Closes #210
Refs #57

Summary

• Replace the bare "disable SELinux temporarily" advice in the CentOS LAMP and LEMP install guides with actionable policy steps that let users run with SELinux enforcing:
  • setsebool -P httpd_can_network_connect 1 and httpd_can_network_connect_db 1 (required for DB access and SNMP polling)
  • semanage fcontext / restorecon commands for non-default install paths
• Fix broken/malformed URL: https:////wiki.centos.org/es/HowTos/SELinux → current RHEL 9 SELinux docs
• Add CentOS EOL banners to both guides: CentOS 7 EOL June 2024, CentOS 8 EOL December 2021; point users to Rocky Linux / AlmaLinux
• Rename Install-Under-CentOS_{LAMP,LEMP}.md → Install-Under-RHEL-Compatible_{LAMP,LEMP}.md; update README ToC
• Replace yum with dnf throughout (yum deprecated in RHEL 8+)
• Fix Spine build: add missing package install step for RHEL 8+; distinguish powertools (RHEL/Rocky 8) vs crb (RHEL/Rocky 9)
• Remove innodb_file_format, innodb_large_prefix, innodb_additional_mem_pool_size (removed MySQL 8.0)
• LEMP nginx: remove TLS 1.0/1.1 (RFC 8996); remove DH+3DES (Sweet32, CVE-2016-2183); add TLS 1.3; enable ssl_prefer_server_ciphers
• LEMP nginx: uncomment HTTP→HTTPS redirect (was silently a no-op)
• LEMP: fix cacti.sql import path and poller.php cron path to use /usr/share/nginx/html

Test plan

• Verify setsebool commands are correct for RHEL 8/9, Rocky 8/9, AlmaLinux 8/9
• Verify RHEL docs URL resolves
• Verify EOL dates against https://endoflife.date/centos
• Verify nginx TLS config is valid for nginx 1.20+

[Copilot]

Pull request overview

Updates the CentOS-based LAMP/LEMP installation docs to reflect CentOS Linux EOL status and to provide actionable SELinux steps that allow running Cacti with SELinux enforcing.

Changes:

• Added CentOS 7/8 EOL notices and guidance to use Rocky Linux/AlmaLinux.
• Replaced “disable SELinux” guidance with SELinux booleans + file-context (semanage/restorecon) steps and updated the SELinux docs link.
• Standardized the LEMP SELinux section structure and updated the non-default install-path note to reference the new steps.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
Install-Under-CentOS_LEMP.md	Adds EOL banner and replaces SELinux section with enforcing-friendly booleans + fcontext/restorecon guidance.
Install-Under-CentOS_LAMP.md	Adds EOL banner, updates SELinux guidance similarly, and links the non-default path note back to the SELinux steps.

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[somethingwithproof]

Both LAMP and LEMP guides already include the policycoreutils-python-utils prerequisite (dnf install -y policycoreutils-python-utils) before the semanage fcontext step. No further changes needed; resolving.