Document $settings['deployment_identifier'] (and that it fixes moved class autoloader caching)

The deployment_identifier was adding in #2507509: Service changes should not result in fatal errors between patch or minor releases → , it started in this comment, #2507509-16: Service changes should not result in fatal errors between patch or minor releases →

Does anyone have suggested wording to add?

Does changing the identifier fix cases like 🐛 Class "Doctrine\Deprecations\Deprecation" not found Active , where a file tree relocates without namespace changes?

Updated the IS.

What text do you want to add?

I'd like to see an example of what the value for the identifier might be if the update was not related to a core Drupal update.

> Document this by adding a deployment example script that includes creating this.

I'm not sure what that would look like.

> I'd like to see an example of what the value for the identifier might be if the update was not related to a core Drupal update.

Agreed, I think it would be worth explicitly saying that the value is arbitrary and that all that matters is that it is changed.

As per #3492523-40: Class "Doctrine\Deprecations\Deprecation" not found → while this does automatically invalidate the container, I'm not convinced that it affects the autoloader.