Oban log setting in databse set to empty string instead of false causing Pleroma to immediately crash on startup (clarification + fix of issue 2826)

I have a (hopefully permanent) fix for issue 2826 that I filed preivously and closed

This turned out to be due to a db config param having Oban log value = "" instead of a valid value of false, or log level string. It was causing Pleroma to crash on startup.

I created a migration to fix this. It's not that easy to manually change these values in the db due to being bytea. Easier to do with a migration rather than guess at the encoding.

Submitting a PR for this branch

Unfortunately this may not be a perfect fix, because the odd thing is, my instance was running fine after updaing to latest stable, then I saved admin settings, THEN it wouldn't restart. So I suspect saving the admin settings somehow set log = "" or triggered this in another way. Hopefully it's all good now though

Thanks!!