Package registry as proxy of package-storage

[mrodm]

Fixes elastic/kibana#145582

This PR changes the behaviour of the requests performed against package-storage.elastic.co. Instead of being a http redirect (CODE 301), it has been changed to perform the actual request against package-storage and forward the contents/headers to the user.

Example of the request when this was applied to proxy mode:

 $ curl -o file.zip -v "http://localhost:8888/epr/elastic_package_registry/elastic_package_registry-0.0.1.zip"
*   Trying 127.0.0.1:8888...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0* Connected to localhost (127.0.0.1) port 8888 (#0)
> GET /epr/elastic_package_registry/elastic_package_registry-0.0.1.zip HTTP/1.1
> Host: localhost:8888
> User-Agent: curl/7.81.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Cache-Control: max-age=600
< Cache-Control: public
< Content-Length: 655945
< Content-Type: application/zip
< Last-Modified: Tue, 26 Jul 2022 17:36:46 GMT
< Date: Thu, 24 Nov 2022 14:59:42 GMT
< 
{ [16384 bytes data]
100  640k  100  640k    0     0  1602k      0 --:--:-- --:--:-- --:--:-- 1605k
* Connection #0 to host localhost left intact

[elasticmachine]

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• Start Time: 2022-12-02T13:06:21.853+0000

• Duration: 5 min 58 sec

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