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/contribution/docs.md

@@ -365,7 +365,7 @@ import TabItem from '@theme/TabItem';
 
     ```bash
     curl -L -X POST '<BACKEND_URL>/admin/uploads' \
-      -H 'Authorization: Bearer <API_TOKEN>' \
+      -H 'x-medusa-access-token: <API_TOKEN>' \
       -H 'Content-Type: text/csv' \
       -F 'files=@"<FILE_PATH_1>"'
     ```