Fix date type update (#9700)

This PR fixes a problem with how TypeORM handles date without time. 

A date without time that is stored in PostgreSQL database as `date` type
gets returned as an ISO string date with a timezone that can shift its
date part in an unwanted way.

In short DB stores `2025-01-01`, TypeORM query builder returns
`2024-12-31T23:00:00Z` which gets parsed as `2024-12-31` on the front
end field.

We don't want to handle timezone here because we are manipulating a date
without its time part, so this PR adds a step that counteracts what
TypeORM does and returns `2025-01-01T00:00:00.000Z` so that the front
can parse it correctly.

@Weiko We might want to check other places of the backend where date
types are returned by TypeORM, we might have the same problem, this PR
only fixes it for updateOne resolver return.

- Fixed date persist on frontend which was shifting the date to a
different day due to timezone issue
- Fixed date returned by the backend update logic, which was shifting
the date by the timezone offset (so this PR adds back the offset so that
it stays at 00:00:00Z time)

packages/twenty-server/src/utils/date/isDate.ts

@@ -0,0 +1,3 @@
+export const isDate = (date: any): date is Date => {
+  return date instanceof Date;
+};

packages/twenty-server/src/utils/date/isValidDate.ts

@@ -0,0 +1,3 @@
+export const isValidDate = (date: any): date is Date => {
+  return date instanceof Date && !isNaN(date.getTime());
+};