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

**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.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)
```

Start in DefinitionLoader.BuildObjectInputAction and inspect how the YAML example's Headers value is assigned to Conductor.Steps.HttpRequest, referenced in HttpRequest.cs. Reproduce the workflow with the supplied definition and verify that a dictionary input works without the JObject conversion error.

Written by the indexing model from the issue text.