Update all curl documentation examples and references with new x-medusa-access-token header (#6326)

## What

This is to update incorrect documentation in regards to authentication to the Admin API - raised in https://github.com/medusajs/medusa/issues/6264.

## Why

Because the current documentation has been incorrect since the September 2023 release of [v1.17.0](https://github.com/medusajs/medusa/releases/tag/v1.17.0), which had breaking changes to API token usage.

## How

Simple search and replace. I was asked to replace occurrences under `www/apps/docs/content/` but there were also additional places where I thought references should also be updated:

- `packages/medusa/src/api/`
- `www/apps/api-reference/`

Feel free to revert them as needed.

There is also some inconsistency between the format shown in examples e.g. `<API_TOKEN>` vs `{api_token}` vs `{access_token}`.

I have kept the format the same in all cases as the original, as surrounding documentation text would not have format updated as well. I suggest maybe reviewing the documentation and keeping to a consistent format e.g. `<API_TOKEN>`.

 
## Testing 

I have not tested these changes. I would assume the `packages/medusa/src/api/` changes may need more thorough testing?

www/apps/docs/content/modules/multiwarehouse/admin/manage-reservations.mdx

@@ -128,7 +128,7 @@ You can list all reservations in your store by sending a request to the [List Re
 
     ```bash
     curl -L -X GET '<BACKEND_URL>/admin/reservations' \
-    -H 'Authorization: Bearer <API_TOKEN>'
+    -H 'x-medusa-access-token: <API_TOKEN>'
     ```
 
   </TabItem>
@@ -223,7 +223,7 @@ You can create a reservation by sending a request to the [Create Reservation API
 
     ```bash
     curl -L -X POST '<BACKEND_URL>/admin/reservations' \
-        -H 'Authorization: Bearer <API_TOKEN>' \
+        -H 'x-medusa-access-token: <API_TOKEN>' \
         -H 'Content-Type: application/json' \
         --data-raw '{
             "location_id": "<LOC_ID>",
@@ -316,7 +316,7 @@ You can update a reservation by sending a request to the [Update Reservation API
 
     ```bash
     curl -L -X POST '<BACKEND_URL>/admin/reservations/<RESERVATION_ID>' \
-        -H 'Authorization: Bearer <API_TOKEN>' \
+        -H 'x-medusa-access-token: <API_TOKEN>' \
         -H 'Content-Type: application/json' \
         --data-raw '{
             "quantity": 3
@@ -401,7 +401,7 @@ You can delete a reservation by sending a request to the [Delete Reservation API
 
     ```bash
     curl -L -X DELETE '<BACKEND_URL>/admin/reservations/<RESERVATION_ID>' \
-        -H 'Authorization: Bearer <API_TOKEN>'
+        -H 'x-medusa-access-token: <API_TOKEN>'
     ```
 
   </TabItem>