companion: pass `endpoint` and `region` to AWS SDK constructor (#2113)

Accidentally removed in #2030. This can cause S3 to reject uploads.

packages/@uppy/companion/src/companion.js

@@ -231,6 +231,8 @@ const getOptionsMiddleware = (options) => {
 
     const s3ClientOptions = Object.assign({
       signatureVersion: 'v4',
+      endpoint: s3ProviderOptions.endpoint,
+      region: s3ProviderOptions.region,
       // backwards compat
       useAccelerateEndpoint: s3ProviderOptions.useAccelerateEndpoint
     }, rawClientOptions)