[Hackday][2.7] Added deprecation trigger

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #12608
| License       | MIT
| Doc PR        |
@nicolas-grekas Do you need the hole classname with namespace included?