chore(oas): replace requestBody with $ref to req class JSDoc OAS (#2867)

### What

Move inline OAS requestBody schema declaration under their respective class-validator classes in order to expose them through  `#/components/schemas`. Replace inline OAS requestBody schema with a `$ref` reference pointing to the newly declared schema.

### Why

Having requestBody declared as its own "named" schema will allow OAS code generators to output typed entities/DTO that can be manipulate without having to reference the route/operation.

### How

Declare a new @schema JSDoc for each class-validator used to parse and validate request body. Move the current inline requestBody to the new @schema.

### Test

- Ran OAS validator.
- Ran docs build script.

Expect no visible changes to the documentation.

### Out-of-scope

requestBody of type `multipart/form-data` used for file uploads. These will be address as part of CORE-934
- [create-upload.ts](https://github.com/medusajs/medusa/blob/58d23a7b45b6dde8bdeed0bb268139a0017f1649/packages/medusa/src/api/routes/admin/uploads/create-upload.ts#L87-L90)
- [create-protected-upload.ts](https://github.com/medusajs/medusa/blob/58d23a7b45b6dde8bdeed0bb268139a0017f1649/packages/medusa/src/api/routes/admin/uploads/create-protected-upload.ts#L87-L90)

Path Parameter and Query Parameter. These will need more research and experimentation, part of CORE-931

---

Resolves CORE-853

packages/medusa/src/api/routes/admin/auth/create-session.ts

@@ -20,19 +20,7 @@ import { validator } from "../../../../utils/validator"
  *   content:
  *     application/json:
  *       schema:
- *         type: object
- *         required:
- *           - email
- *           - password
- *         properties:
- *           email:
- *             type: string
- *             description: The User's email.
- *             format: email
- *           password:
- *             type: string
- *             description: The User's password.
- *             format: password
+ *         $ref: "#/components/schemas/AdminPostAuthReq"
  * x-codeSamples:
  *   - lang: JavaScript
  *     label: JS Client
@@ -113,6 +101,22 @@ export default async (req, res) => {
   }
 }
 
+/**
+ * @schema AdminPostAuthReq
+ * type: object
+ * required:
+ *   - email
+ *   - password
+ * properties:
+ *   email:
+ *     type: string
+ *     description: The User's email.
+ *     format: email
+ *   password:
+ *     type: string
+ *     description: The User's password.
+ *     format: password
+ */
 export class AdminPostAuthReq {
   @IsEmail()
   @IsNotEmpty()