Multi-network Support

## Story
As a user
I want view network stats for testnets
So that I can gain insights into the state of testnets

## Background

Currently the application is focused on the Beacon Chain. It would be nice, and fairly trivial, to enable it to crawl and gather stats for all testnets.

## Details

N/A

## Scenarios
N/A

## Implementation details

The necessary changes appear to be:
- Allow bootnodes to be specified at runtime (currently hardcoded)
- Modify front end to indicate which network is being shown and potentially show/hide certain elements that may be network-specific

## Testing details

N/A

## Acceptance criteria

We can deploy a second instance of the application that shows the latest stats for Kintsugi merge-net.