feat: fix doc warnings by Vale acronym rule

What does this MR do and why?

This MR continues to solve #276199 (closed) by adding frequently occurring acronyms to the list. Acronyms that appear to less frequent are expanded.

File Change

• doc/.vale/gitlab/Acronyms.yml
• doc/administration/auth/index.md
• doc/administration/postgresql/replication_and_failover.md
• doc/administration/nfs.md
• doc/administration/smime_signing_email.md

Acronym

• ELB - Elastic Load Balancing
• LTM - Load Traffic Manager
• PID - Process Identification Number
• RDS - Relational Database Service
• SAN - Subject Alternative Name
• UID - User Identifier

MR acceptance checklist

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