[Feature Request] Add optional bind IP option (--interface) when using curl

[taoky]

When StorageMirrorServer.jl is used under an environment with multiple IPs (interfaces) from different ISPs, it could happen that upstreams (https://us-east.storage.juliahub.com and https://kr.storage.juliahub.com) are only reachable under some specific interfaces (it could happen when some ISPs block upstreams' IPs).

curl (as is used in v0.2.0) supports binding to a specified interface when requesting, by adding a parameter --interface. It can be designed that when a specific environment variable (e.g., BIND_ADDRESS=xxx.xxx.xxx.xxx) is set, then use it to request upstreams (curl --interface $BIND_ADDRESS ...). Configuring Julia's storage syncing can be more flexible if it can be implemented.

[johnnychen94]

Will be available in v0.2.1