Add query parameters to workflow input

[siva-sai-udaygiri]

This PR fixes the start workflow API so query parameters passed in the request URL are added to the workflow input.

Before this change, a request like:

POST /api/workflow?url_param=1234

with body input:

{
  "name": "test_workflow",
  "input": {
    "first": "xyz"
  }
}

would start the workflow with only the body input:

{
  "first": "xyz"
}

Because of that, ${workflow.input.url_param} was not available during workflow execution.

With this change, query parameters are merged into StartWorkflowRequest.input before the workflow is started, so the workflow input becomes:

{
  "first": "xyz",
  "url_param": "1234"
}

The implementation also handles cases where the request input is null by creating an input map before adding query parameters.

Added a unit test to verify that the controller passes the updated StartWorkflowRequest to WorkflowService with both the original body input and query parameter values included.