support longblob in mysql

[hunjixin]

Summary

support longblob in mysql

Motivation

blob is small, need long blob to store vec

Additional Information

[billy1624]

Hey @hunjixin, sorry for the delay. Yes, we definitely can bring this to SeaORM

• https://github.com/SeaQL/sea-query/pull/314

Please check this PR I just created:

• https://github.com/SeaQL/sea-orm/pull/850