Support OpenRPC Spec 1.3.2 in Playground

[jamesabbottsmith]

First off - thanks for doing this work, it looks great and I'm looking forward to using it.

I've encountered an issue when describing notifications in the playground.

It appears that notifications were not originally included in the OpenRPC spec but were added following open-rpc/spec#230 and included in v1.3.0. However, this version of the OpenRPC spec does not appear to be supported in the playground, which currently allows up to

Reproduction:
Open the playground, and try the example found here
https://github.com/open-rpc/examples/blob/master/service-descriptions/metrics-openrpc.json

Ideal resolution:
Update the playground to support the latest OpenRPC spec.
(Ideally, this would also include updating the VSCode plugin as well)