pin remote add: improve Peer hints in Pin.origins

[lidel]

go-ipfs 0.8.0-rc2 adds pin remote commands (details in #7559).

When a new remote pin is added via pin remote add Pin.origins array is populated with all multiaddrs of the local node.

Problem

This is a bit naive, because:

• local node may not have the data
• most of multiaddrs are LAN ones and not diallable from the outside (and if service is in LAN, then it does not need them, mdns/land DHT will do just fine)

Proposed improvements

1. Check if pinned root CID is in local blockstore. If it is not, then send empty Pin.origins = []
   (local node is not origin, we are pinning some external CID, eg. when DAG is too big to fit on local laptop)
   CLI prior art:

   $ ipfs block stat --offline $cid
   Error: blockservice: key not found

2. Filter out IP multiaddrs from loopback addres (https://golang.org/pkg/net/#IP.IsLoopback) and maybe networks designated as local/LAN/private: https://en.wikipedia.org/wiki/Private_network

[bisakhmondal]

Hey @lidel, I want to give it a try, can I?
I suppose from a top-level look,
https://github.com/ipfs/go-ipfs/blob/cd72589cfd41a5397bb8fc9765392bca904b596a/core/commands/pin/remotepin.go#L176-L179
this need to be updated.
Thanks :)

[lidel]

@bisakhmondal yes, sounds about right.

I believe we should:

• filter out loopback addres via IP.IsLoopback
• filter out addrs that match denylist defined in config under NoAnnounce

This way people who want to use private networks, still can.