[ci skip] Update guides license to CC BY-SA 4.0 International.

Benefits: https://creativecommons.org/version4
Added link for 4.1 guides on edge guide [ci skip]
Tiny follow up to #14915 [ci skip]
Automaticly add username and email if configured in git-scm, as bundle gem
Works correctly if git not installed
skip-git should not hit git commands plugin generators
Merge pull request #14941 from arunagw/hbakhtiyor-new-plugin-command-advanced-config

Plugin gemspec
Merge pull request #14942 from JuanitoFatas/patch/cc-by-sa-4-0

[ci skip] Update guides license to CC BY-SA 4.0 International.
Add singular and plural form for some validation messages
Merge pull request #14943 from arunagw/hbakhtiyor-i18n-validation-message-singular-and-plural

Add singular and plural form for some validation messages
eliminate repetition in guide links for past releases [ci skip]