When using YAML / JSON workflow definition, input type is forced to JObject

[heisk3478]

Describe the bug
When using yaml / json workflow definition, DefinitionLoader.BuildObjectInputAction method will convert dictionary to JObject.
Which means we can't use dictionary as the input type in any step class. Basically https://github.com/danielgerlag/conductor/blob/master/src/Conductor.Steps/HttpRequest.cs#L21 won't work with yaml definition.

To Reproduce
The following yaml will fail since Headers section will be converted to JObject.

    StepType: Conductor.Steps.HttpRequest, Conductor
    Inputs:
      BaseUrl: '"https://reqres.in/"'
      Resource: '"/api/login"'
      Method: '"POST"'
      Headers:
        "@apiKey": environment["LOGNAME"]

Expected behavior
Dictionary type input should work with yaml workflow definition.

Additional context
Error message:

Object of type 'Newtonsoft.Json.Linq.JObject' cannot be converted to type 'System.Collections.Generic.IDictionary`2[System.String,System.Object]'.

Stacktrace:

   at System.RuntimeType.CheckValue(Object& value, Binder binder, CultureInfo culture, BindingFlags invokeAttr)
   at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, Object[] index)
   at WorkflowCore.Services.DefinitionStorage.DefinitionLoader.<>c__DisplayClass12_0.<BuildObjectInputAction>g__acn|0(IStepBody pStep, Object pData, IStepExecutionContext pContext)
   at WorkflowCore.Models.ActionParameter`2.Assign(Object data, IStepBody step, IStepExecutionContext context)
   at WorkflowCore.Models.ActionParameter`2.AssignInput(Object data, IStepBody body, IStepExecutionContext context)
   at WorkflowCore.Services.WorkflowExecutor.ExecuteStep(WorkflowInstance workflow, WorkflowStep step, ExecutionPointer pointer, WorkflowExecutorResult wfResult, WorkflowDefinition def, CancellationToken cancellationToken)