Changes

open5gs-latest: fix Dockerfile: avoid using curl for downloading keys

Since recently, curl fails to download the key from www.mongodb.org:

'''
$ curl --verbose https://www.mongodb.org/static/pgp/server-4.2.asc
GET /static/pgp/server-4.2.asc HTTP/1.1
Host: www.mongodb.org
User-Agent: curl/7.82.0
Accept: */*

Mark bundle as not supporting multiuse
HTTP/1.1 301 Moved Permanently
Content-Type: text/html
Date: Wed, 13 Apr 2022 20:50:19 GMT
Location: https://pgp.mongodb.com/server-4.2.asc
Connection: Keep-Alive
Content-Length: 0
'''

By default, curl would not follow redirects unless '-L' is specified.
Let's use Docker's 'ADD' command instead, like many Dockerfiles do.
Also, update the address as suggested in the server's response.

Change-Id: I9757fcce084595341b1a68822bad454b64941eb1
Related: SYS#5602