Sink interceptor type

[BobDickinson]

In implementing the TypeScript SDK we ran into the following issue. The SEP defines the interceptor types as:

  /**
   * Interceptor operation type
   */
  type: "validation" | "mutation";

The C# SDK also implements a type called sink:

    /// <summary>
    /// Fire-and-forget, non-blocking, non-mutating interceptor type for reacting to context
    /// (logging, telemetry, avatar animation, voice-mode triggers, etc.) without affecting
    /// the interaction. Sink interceptors run in parallel and failures are swallowed.
    /// </summary>
    [JsonStringEnumMemberName("sink")]
    Sink,

The TypeScript SDK implements sink for compatibility with the C# SDK.

We should either officially add sink to the spec/SEP, or remove it from all SDKs.