When the APCu extension is installed, Doctrine will automatically use it for metadata and query caches. This means a speedup for our applications since the Doctrine Entity metadata (mapping to the database) does not have to be parsed & processed on every request.
Acceptance criteria:
* APCu PHP extension is installed both on UAC and production system (using our infrastructure playbooks)
* Cache is automatically cleared on deployment (using our deployment playbooks)
Notes:
* This ticket depends on {T247746} and {T247745}, because they'll use the Doctrine `Setup` class instead of FundraisingStore to set up the entity manager.
* The package name is `php-apcu`, the name is the [[ https://github.com/oerdnj/deb.sury.org/wiki/Frequently-Asked-Questions#why-are-some-packages-named-phpxy--and-some-php- | same for all PHP versions ]].