fix: #3589035 DomainConfigMigration: rescue legacy 2.x rows the original regex left behind

Frank Mablyrequested to merge
issue/domain-3589035:3589035-patch-domainconfigmigration-to into 3.0.x

fix: #3587744 domain_config: Make DomainConfigOverrideEditable::save() write a sparse, cast-aware diff against base

By: mably

Closes #3589035

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