This change fixes two different problems.
First, we add a data migration to migrate the configuration of sites using Open AI's embedding model. There was a window between the embedding config changes and #1087, where sites could end up in a broken state due to an unconfigured selected model setting, as reported on https://meta.discourse.org/t/-/348964
The second fix drops pre-seeded search indexes of the models we didn't migrate and corrects the ones where the dimensions don't match. Since the index uses the model ID, new embedding configs could use one of these ones even when the dimensions no longer match.
a53719ab8e