Improve user-experience when encountering unknown or corrupted SO documents during a migration

[pgayvallet]

Part of #126672
Part of #129016

At the moment, when unknown or corrupted saved object documents are encountered during a migration, it forces the user to manually interact with the Kibana system indices to either fix or remove them before reattempting the migration.

In the scope of #126672, we'll want to:

• Add a new migration.ignoreCorruptObjects (name TBD) that would just ignore the faulty documents during migration when enabled (disabled by default)
• Allowlist this new config option for cloud customers

Also, in the scope of #129016, we should:

• Assign a specific error code to this failure
• Add online documentation describing how to fix, or work around, the failure
  • how to manually delete/fix the doc AND/OR
  • how to use the new migration config option we'll be implementing in the scope of this issue
• Surface the error code, and the link to the documentation, in the failure's log

Open questions:

• should we archive the faulty documents somewhere when the migration.ignoreCorruptObjects option is enabled?
  • Given we will not remove them from the old version's index, it feel acceptable to not do that
• do we need to output more data when listing the corrupted documents in the logs?
  • Given we'll link to documentation that will explain how to retrieve the documents to fix them, I'd say this is probably unnecessary too

[elasticmachine]

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