SavedObjects: Add migration script to ensure no empty IDs

[afharo]

Related to #146345 and #120693.

#120693 added a validation so Saved Objects cannot be created without an ID. However, when upgrading from previous versions, we may keep those IDs empty. This may eventually break when exporting and importing the SOs.

We should create a migration script to ensure all migrated documents have an ID.

N.B.: Mind the references from other SOs.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[pgayvallet]

We should create a migration script to ensure all migrated documents have an ID.

Just my 2cts, but global migrations and coreMigrationVersion were ihmo a terrible mistake only currently used for shareable-SO types ID rewrites.

Unless we think the risk of such ID-less document for our system is very high (e.g if such documents can be created by internal features and not only by external calls to our APIs and/or tampering with export files), I would restrain from implementing such 'core' migration.

[afharo]

I agree that manually tampered documents should not be of our concerns (especially since there are already measures to ensure they are not created in recent versions).

However, somehow, we managed to break Kibana by importing documents with empty IDs (#146345). Probably fixing that issue I linked is just enough for now.

[TinaHeiligers]

... empty IDs (#146345). Probably fixing that issue I linked is just enough for now.

Sounds to me like extending validation on objects being imported/created might work. An extension of #118969? Then again, I haven't seen any other issues with import/export docs with empty ID's yet.

[afharo]

I think we all agree that fixing #146345 might just be enough. I'll go ahead and close this issue. Feel free to reopen it if there's something I missed.