GTM dataLayer parameter should take an object, not an array of strings (

#66339)

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fixes #64364 

As noted in the bug, the `dataLayer` parameter to the GoogleTagManager
third-party component should be an object (which gets passed to
`JSON.stringify()` at
https://github.com/vercel/next.js/blob/canary/packages/third-parties/src/google/gtm.tsx#L43),
and not an array of strings.

(I'm speculating a bit, but assuming that the original intent was that
an object could be serialized and passed to the component, but then the
call to stringify was added to the component as well.)

I'm not thrilled about duplicating the JSONValue type, which also exists
in `packages/next/src/server/config-shared.ts`, but wasn't sure whether
it would be preferred to export from there -- this doesn't feel like
it's likely to be an issue, but I'm perfectly happy to change

---------

Co-authored-by: Sam Ko <sam@vercel.com>

packages/third-parties/src/types/google.ts

@@ -5,9 +5,16 @@ declare global {
   }
 }
 
+type JSONValue =
+  | string
+  | number
+  | boolean
+  | JSONValue[]
+  | { [key: string]: JSONValue }
+
 export type GTMParams = {
   gtmId: string
-  dataLayer?: string[]
+  dataLayer?: { [key: string]: JSONValue }
   dataLayerName?: string
   auth?: string
   preview?: string