Improve the API for configuring roster properties of a node

The test writer should be able to specify all properties of a node's roster entry in a fluent style, like this:

```
network.addNode()
.id(1)
.weight(1)
.keyAndCert(...)
.gossipIP(...)
.gossipPort(...);
```
Such an API will eliminate the need for the `OtterSpecs(randomNodeIds = true/false)` attribute.

These fields should also come with the ability to set a generator:

- Node ID (consecutive IDs, or non-consecutive randomized (default))
- Weight (default generator or custom generator)
- Keys and Certs (random keys and certs (default?), or deterministic by node id)

Start by locating the test-network entry point for network.addNode() and the OtterSpecs randomNodeIds setting, then trace how roster properties and their generators are currently configured. Done means a fluent API covers node IDs, weights, keys and certificates, gossip IPs and ports, including the listed generator choices, without requiring the OtterSpecs attribute.

Written by the indexing model from the issue text.