setValue(key) {
      this.spanKey = key
    }
Called before setting up the otel bridge ContextManager.
This creates a fake context and uses the otel api to set a span.
By creating a fake `setValue` when it will give us the symbol used for enqueueing spans to the context.
This is assigned as a key on the agent.
We will use this key to enqueue our FakeSpan when we enter a segment or transaction so that when using otel API it will return the appropriate traceId and spanId.

@param {Agent} agent instance