Client customization late-join spawner priority for arrivals/cryostorage (#24586)

Client customization late-join spawner priority for arrivals/cryostorage (#24586)

* Initial commit, requires server restart to take effect

* Exposes callbacks directly instead, takes effect immediately

* Cleaned up control flow, swapped cvar for client customization

* Switched to int, dictionary of callbacks, migration

* Update Content.Shared/Preferences/SpawnPriorityPreference.cs

* krunkle stan

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Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>
Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>