Squash migrations for better performance

[matmair]

We currently ship a lot of migrations that are run in order; even on new instances. I suggest shipping 1.0 with squashed migrations and removing the old migrations with the next version. There would need to be a check that versions below 0.x can not be upgraded to a version > 1.x

[matmair]

I made a POC of how that could look like. For this to happen we need at least a week or so of database change freeze to
a) make the patch (will take a few hours probably)
b) have the change running for a few days to be sure it does not destroy instance

[SchrodingersGat]

@matmair that looks nice, I was expecting we'd have to have a breaking change here but, if I read it correctly, this is a "drop in" replacement for an existing setup?

I'd like to ensure we have #4973 working before this point

[matmair]

@SchrodingersGat yes, that is the idea. Will speed up startups as well in my experience.

[matmair]

@SchrodingersGat I would start working on this if there are no objections. Is this clear to go?

[SchrodingersGat]

@matmair sounds good :) We will have to treat this one very carefully

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