docs: updates to use DML and other changes (#7834)

- Change existing data model guides and add new ones for DML
- Change module's docs around service factory + remove guides that are now necessary
- Hide/remove all mentions of module relationships, or label them as coming soon.
- Change all data model creation snippets to use DML
- use `property` instead of `field` when referring to a data model's properties.
- Fix all snippets in commerce module guides to use new method suffix (no more main model methods)
- Rework recipes, removing/hiding a lot of sections as a lot of recipes are incomplete with the current state of DML.


### Other changes

- Highlight fixes in some guides
- Remove feature flags guide
- Fix code block styles when there are no line numbers.

### Upcoming changes in other PRs

- Re-generate commerce module references (for the updates in the method names)
- Ensure that the data model references are generated correctly for models using DML.
- (probably at a very later point) revisit recipes

www/apps/book/app/advanced-development/admin/widgets/page.mdx

@@ -75,9 +75,12 @@ Widgets that are injected into a details page (for example, `product.details.aft
 
 For example:
 
-```tsx title="src/admin/widgets/product-widget.tsx" highlights={[["5"]]}
+```tsx title="src/admin/widgets/product-widget.tsx" highlights={[["8"]]}
 import { defineWidgetConfig } from "@medusajs/admin-shared"
-import { DetailWidgetProps, AdminProduct } from "@medusajs/types"
+import { 
+  DetailWidgetProps, 
+  AdminProduct,
+} from "@medusajs/types"
 
 const ProductWidget = ({ 
   data,