Include HTTP and WebSocket endpoints in construct

The goal of this feature is to fetch the `HTTP` and `WebSocket` endpoints created for each node to include them in this custom Ethereum node construct. By including these endpoints within the construct, developers will be able to further integrate their Ethereum nodes in the form of CDK outputs for use with other AWS resources, all encapsulated in an AWS CDK application. See a node instantiation example of the endpoints below.

```
const node = new EthereumNode(this, 'ExampleNode', {
network: NetworkId.ROPSTEN,
availabilityZone: 'us-east-1a',
instanceType: InstanceType.BURSTABLE3_XLARGE,
});
```

Calling the ```node``` endpoint property would yield an output such as:

``` node.httpEndpoint = nd-XXXXXXXXXXXXXXXXXXXXXXXXXX.ethereum.managedblockchain..amazonaws.com ```

or

``` node.webSocketEndpoint = nd-XXXXXXXXXXXXXXXXXXXXXXXXXX.wss.ethereum.managedblockchain..com```