Help/About: Add help tabs to provide informations about plugin & themes auto-updates.

Adds language around how the feature works and includes links to the WordPress HelpHub pages.

Fixes: #50215.
Props: audrasjb, garrett-eclipse, paaljoachim, marybaum, pbiron, whyisjake.


Built from https://develop.svn.wordpress.org/trunk@48062


git-svn-id: https://core.svn.wordpress.org/trunk@47829 1a063a9b-81f0-0310-95a4-ce76da25c4cd