support an array of url for a single leafnode remote

[ripienaar]

• Feature Request or Change Proposal

Use Case:

Today leafnodes take a single seed url and then rely on discovery to find the rest of the cluster for failover. This dynamic nature is problematic for more enterprise orientated setups or just people who prefer clarity in configuration == reality. Further if the seed node is down for maintenance or due to failure its trouble and would then require config changes etc.

Gateways accept both a url and urls, the intention is that you'd give it a number of remote hosts in the same single leafnode remote and have it try to connect to any of those.

Proposed Change:

Support this:

leafnodes {
    remotes = [ 
        { urls: nats-leaf://r2:4000, nats-leaf://r1:4000, 
          credentials: /Users/synadia/.nkeys/O/accounts/A/users/leaf.creds 
        },
    ]
}