fix: change character limits to allow for long instance domains

This PR changes the max length for hosts of various entities to 512 characters, and the max length of favicon and icon URLs for instances to 4096 characters, to allow federation to work properly with instances that have long domains such as this one.

I wrote the migration by hand as typeorm's generator prefers to delete tables instead of updating them.

I'm unsure if this is the best way to handle this, but i've tested it and it works. Open to suggestions.

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