[Tracker] 2.0 release

[jordy25519]

The 2.0 release updates @polkadot/* packages major version.
The javascript module system now supports ESM.
This should be the default going forward and can be used with node >= 14versions by specifying "type": "module" in package.json.

• Announce 2.0 upgrade guide + plan
• Remove @cennznet/util Remove @cennznet/util #243
• Update subscribe test with published 2.x version
  ~Improve discoverability of API methods #286 ~