Bail during start-up if there are old background updates.

[matrixbot]

This issue has been migrated from #16397.

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This is a basic implementation to enforce that some old background updates have run.

My hope is that this could be used to avoid future situations like #16192. This would fix #16047 in a simplistic manner and doesn't attempt to differentiate between different types of background updates.

This still would require us to do thinking about what old updates are now required, but I think it would fix the issue where we have to continually create background jobs due to dependencies.

TODO

• Enforce that ordering is filled in (non-nullable).
• Maybe try to fix that BACKGROUND_UPDATES_COMPAT_VERSION < last full schema dump?
• Documentation.