access-client CLI should tell users if they're using an unsupported version of node

[travis]

I was using node 16.3.1 and tried to run the CLI - setup worked but whoami and create-space did not:

➜  access-client git:(main) ✗ node ./src/cli/index.js setup
Path: [elided]w3access/main.json
? Input the name for this device: lappy
? Select this agent type: device
Agent is ready to use.
➜  access-client git:(main) ✗ node ./src/cli/index.js whoami
file:///[elided]/w3protocol/packages/access-client/src/agent.js:61
        fetch: options.fetch ?? globalThis.fetch.bind(globalThis),
                                                 ^
TypeError: Cannot read properties of undefined (reading 'bind')
[elided]

➜  access-client git:(main) ✗ node ./src/cli/index.js create-space
file:///[elided]/w3protocol/packages/access-client/src/cli/utils.js:28
    const rsp = await fetch(url + 'version')
                ^
ReferenceError: fetch is not defined

After upgrading to node 19.2 things started working.

I think we should 1) document which versions work and 2) verify we're using a supported version of Node at runtime and let the user down easy if not.