[saved objects] Type validation enhancements

[lukeelmers]

In #104088 we agreed that for our initial implementation of Saved Objects type validations, we'd stick with validating types during create and bulkCreate operations. This was implemented in #118969

However, in the course of our discussion on the issue, we identified a few possible enhancements to consider for the future:

• Support for update operations. This is tricky because it means suddenly all fields in a provided schema would need to become optional.
• Perform validations inside the migration system. Currently they are happening in the SO repository itself.
• Consider performing validations during each step of migrations. Since validations are currently performed after migrations in create, it means that a migration could fail due to a corrupt object, but instead of getting a useful error message, you'd just get an error from the migration itself. However, this is a departure from how migration functions are currently implemented, so we would need to weigh how we'd approach something like this. More details in [Saved Objects] introduce per-type validation schemas.  #104088 (comment)

[elasticmachine]

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

[pgayvallet]

We're getting closer to removing the SO http APIs, meaning that most of the SO types should have their own set of APIs and service/business layer, so that kind of low-level validation is no longer really needed (nor should be the recommended approach).

I'm going to close this