Added Header support

[Hugo-Persson]

Added support for generating schema for headers and validating headers. Headers can be added to specification like this

		.input({
			headers: z.object({
				"authentication-token": z.string(),
				"x-device-type": z.nativeEnum(DeviceType),
			}),
		})

They are then passed in handler like this:

		.handler(async (_, { headers }) => {

The headers type is automatically inferred.