fix: check if peer is already connected

[im-adithya]

Fixes #394

Checks if the peer is already connected, and returns nil

[bumi]

can we catch the error? then we don't have to always do two calls? because this now takes double the time and it doubles the things that can go wrong.
if the error is that a peer is already connected we treat it as success.

[bumi]

utACK

[rolznz]

I think this is quite fragile error handling:

if grpcErr, ok := status.FromError(err); ok {
		if strings.HasPrefix(grpcErr.Message(), "already connected to peer") {
			return nil
		}
	}

If the error message changes slightly this could break again. Does this particular error have a specific code we can use?

[im-adithya]

The code we get is codes.Unknown, LND doesn't give any specific errors sadly

[rolznz]

utACK

[bumi]

I think this is quite fragile error handling:

I said and think this is OK. because I think it's better than doing a second request to look for the peers with all the addtional error cases and we don't have a code to identify it and I don't think the message changes likely.