Upgrade TiDB without manually Canceling DDL(Phase 2)

[zimulala]

Feature Request

This solution mainly solves Future Works 2 in phase 1. That is, except for the DDL job that is running (when the upgrade starts), all other jobs will only run on the new version of TiDB. In addition, this solution will also solve the unified control problem of the upgrading TiDB process.

Development Plan

• Implement /upgrade/start and upgrade/finish APIs #45886
• Handles parallel execution of upgrade start #46227
• Compatible upgrade with previous versions #46275
• Update /upgrade?op={op} to /upgrade/{op} and update docs #46424
• Simple refactoring code for upgrade #46493
• Implement /upgrade/show API #46460
• Adjust the compatible behavior of this feature #46639
• Before we start or finish this function, disable or enable dist task mode #46892
• Update docs

Ref: #39751