feat: writing varnish chapter

[alemorvan]

Author checklist (Completed by original Author)

• Good fit for the Rocky Linux project? Title and Author Metatags inserted ?
• If applicable, steps and instructions have been tested to work
• Initial self-review to fix basic typos and grammar completed

Rocky Documentation checklist (Completed by Rocky team)

• 1st Pass (Document is good fit for project and author checklist completed)
• 2nd Pass (Technical Review - check for technical correctness)
• 3rd Pass (Detailed Editorial Review and Peer Review)
• Final approval (Final Review)

[alemorvan]

Thx @SergeCroise

[sspencerwire]

@alemorvan Looks great, but let's decide right now if this is a chapter by itself or will need to be broken down as a sub-chapter. (like what has been done with the web and database sections.) If the latter, then we need an introduction for the category, and then sub-chapters for HAProxy and Varnish and any other sections you are going to add. My vote would be for that, because otherwise this document will get VERY long very fast.

[github-actions]

Test results for 170b783:

Number of broken URLs: 3

URL,RESULT,FILENAME
 http://server1.rockylinux.lan,failed,books/web_services/052-load-balancer-proxies-varnish.md
 http://server1.rockylinux.lan:6081,failed,books/web_services/052-load-balancer-proxies-varnish.md
 https://azuremarketplace.microsoft.com/en-us/marketplace/apps/resf.rockylinux-aarch64,failed,guides/cloud/migration-to-new-azure-images.md