feat(oas): declare x-codegen on Admin routes - PRO to R (#3093)

### What

Declare `x-codegen` in OAS for Admin routes - PRO to R.

### Why

We are introducing a new `x-codegen` OpenApi extension, also known as _vendor extension_, in order to help with passing information down to code generators.

In our case, we wish to declare the `method` name that we would expect to call on a client. This mimics our current JS client package. 
E.g. `medusaClient.product.list` where `product` is the tag of the route and `list` is the x-codegen.method value.

We are also defining the name of a potential typed object for query parameters. OAS 3.0 does not allow to bundle query parameters under a single definition but it is not uncommon to see API clients handle all query parameters as a single typed object, like our JS client package. With x-codegen.queryParams, a code generator can create a named and typed object to bundle all query parameters for a given route. 
E.g. `medusaClient.customer.retrieve(id: string, queryParams: AdminGetCustomerParams)` 

### How

Declare `x-codegen` as an object with fields `method` and `queryParams` on all paths.

Match method and queryParams values with equivalent ones from our current JS client package.

### Test

* Ran OAS validator.
* Ran docs build script.

Expect no visible changes to the documentation.

.changeset/twelve-onions-tap.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/medusa": patch
+---
+
+feat(oas): declare x-codegen on Admin routes - PRO to R