Add `Date` as a valid return type for `max` and `min`

[samclearman]

At least with postgres / pg, it's possible for the value of a field generated by the max and min functions to be a Date. This PR updates the constraints on the types of these functions to reflect that.

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Name	Status	Preview	Comments	Updated (UTC)
kysely	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 5, 2025 10:46pm

[igalklebanov]

Hey 👋

Thanks! 💪

~~Let's add a unit test case that verifies a Date is returned by pg @ https://github.com/kysely-org/kysely/blob/master/test/node/src/aggregate-function.test.ts.~~ ~~Let's add type-only test cases @ https://github.com/kysely-org/kysely/blob/master/test/typings/test-d/aggregate-function.test-d.ts.~~

[igalklebanov]

Pushed this through the finish line. Thanks for raising this. 🙏