feat(medusa-react,medusa-js): Allow custom headers (#4409)

* add support for passing custom headers to backend through medusa-js and medusa-react

* switch order of override of headers

* Create gentle-teachers-greet.md

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Co-authored-by: Oliver Windall Juhl <59018053+olivermrbl@users.noreply.github.com>

packages/medusa-react/src/contexts/medusa.tsx

@@ -32,6 +32,7 @@ interface MedusaProviderProps {
    * available within the request
    */
   publishableApiKey?: string
+  customHeaders?: Record<string, any>
 }
 
 export const MedusaProvider = ({
@@ -39,6 +40,7 @@ export const MedusaProvider = ({
   baseUrl,
   apiKey,
   publishableApiKey,
+  customHeaders,
   children,
 }: MedusaProviderProps) => {
   const medusaClient = new Medusa({
@@ -46,6 +48,7 @@ export const MedusaProvider = ({
     maxRetries: 0,
     apiKey,
     publishableApiKey,
+    customHeaders
   })
   return (
     <QueryClientProvider {...queryClientProviderProps}>