Add support for Custom Error Codes

[palamccc]

Motivation

In Java implementation, custom application errors can be thrown using RSocketErrorException. https://github.com/rsocket/rsocket-java/blob/37fc68c68f4b61d826084330a7b0476a456b63da/rsocket-core/src/main/java/io/rsocket/RSocketErrorException.java#L27

But in Js implementation, there is no way to throw custom Errors, All Js Errors are captured and serialized with the same error code APPLICATION_ERROR.

https://github.com/rsocket/rsocket-js/blob/23da9b0e9377ba52d3294cf4763cbbf3de7ba7b1/packages/rsocket-core/src/RSocketMachine.js#L869-L875

Desired solution

Add custom Error class RSocketError and use its error code in the error frame.