fix: console.shorebird.dev insights tab reports times in UTC

[eseidel]

This has come up for a couple users recently, where our reporting in UTC has been confusing to users closely monitoring their patch installs:
#1753 (comment)

[bryanoltman]

This will require changes to how the code push server communicates insights information to the console. Currently, it returns a list of

typedef PatchInstallMetadata = ({
  int patchNumber,
  int installCount,
  DateTime date,
});

Where these are grouped by day on the server side without knowing the client's time zone.

[bryanoltman]

Otherwise, dates on the console seem to be reported correctly in local time

[eseidel]

See also shorebirdtech/updater#131, which is a source of confusion for users.