[no patch] Update the release cycle process overview handbook page for the new major version schedule

Problem/Motivation

#3238652: [policy] Decide how long major Drupal versions should be supported requires updates to core policy documentation.

Proposed resolution

https://docs.google.com/document/d/1btZmsozlxbaIJJmMeH5xvlscVMq8x_CTydjR... is a draft rewrite of the page by the Drupal core release managers.

Remaining tasks

Followup issues needed. Update other pages, including:

• Allowed changes needs a maintenance minor section
• Other handbook pages?
• Announcement