feat: make safe_network examples work with live networks

[happybeing]

Currently examples such as the Registers example (see README) only work on a local testnet. For example:

cargo run --example registers --features=local-discovery -- --user alice --reg-nickname myregister

I tried variations on this command with ValentinesNet with a couple of random peers taken from the log of one of my participating nodes. For example:

export SAFE_PEERS="/ip4/46.101.12.135/udp/42763/quicv1/p2p/12D3KooWQGTGdhfVFHC6zGs7H25F1rdRyoictZYz4VkTqP8qag37"

cargo run --example registers --features=network-contacts -- --user alice --reg-nickname myregister
# and
cargo run --example registers -- --user alice --reg-nickname myregister

I always get the same error:

Starting SAFE client...
Error: Could not connect to the network in 30s

Location:
    sn_node/examples/registers.rs:55:18

It would be useful I think to be able to run examples (that make sense) with a live network. (forum post)