Symfony events for user preference changes

[PVince81]

We already trigger symfony events before and after system config and app config changes.

We should also do so for user preference changes.

@tomneedham @sharidas

[ownclouders]

GitMate.io thinks possibly related issues are #30996 (Throw symfony events on group actions), #30054 ([stable10] Bump symfony/event-dispatcher from 3.2.4 to 3.2.14), #30930 (Add symfony events for delete share), #29885 (Adding new Symfony events), and #30570 ([WIP] Adding symfony events for shares).

[PVince81]

PR here: #31266

[lock]

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