feat(medusa): Rollout index engine behind feature flag (#11431)

**What**
- Add index engine feature flag
- apply it to the `store/products` end point as well as `admin/products`
- Query builder various fixes
- search capabilities on full data of every entities. The `q` search will be applied to all involved joined table for selection/where clauses

Co-authored-by: Carlos R. L. Rodrigues <37986729+carlos-r-l-rodrigues@users.noreply.github.com>

packages/modules/index/integration-tests/__tests__/data-synchronizer.spec.ts

@@ -199,7 +199,7 @@ describe("DataSynchronizer", () => {
         filters: {
           id: [testProductId],
         },
-        fields: ["id", "title"],
+        fields: ["id", "created_at", "title"],
       })
 
       // Second loop fetching products
@@ -225,7 +225,7 @@ describe("DataSynchronizer", () => {
         filters: {
           id: [testProductId2],
         },
-        fields: ["id", "title"],
+        fields: ["id", "created_at", "title"],
       })
 
       expect(ackMock).toHaveBeenNthCalledWith(1, {