[FEATURE] Get Workflow API

[amitgalitz]

Is your feature request related to a problem?

We should have a get workflow API for a specific workflow to complement the search workflows API we currently have

What solution would you like?

The API path should be /_plugins/_flow_framework/workflow/yfRsposBMbAFAhZEJ1qE/ and should return the entire template object stored in the global context index. The response should be similar to the original template given:

{
  "name": "create-connector-register-deploy-model",
  "description": "test case",
  "use_case": "TEST_CASE",
  "version": {
    "template": "1.0.0",
    "compatibility": [
      "2.12.0",
      "3.0.0"
    ]
  },
  "workflows": {
    "provision": {
      "nodes": [
        {
          "id": "workflow_step_1",
          "type": "create_connector",
          "user_inputs": {
            "name": "OpenAI Chat Connector",
            "description": "The connector to public OpenAI model service for GPT 3.5",
            "version": "1",
            "protocol": "http",
            "parameters": {
              "endpoint": "api.openai.com",
              "model": "gpt-3.5-turbo"
            },
            "credential": {
              "openAI_key": "123"
            },
            "actions": [
              {
                "action_type": "predict",
                "method": "POST",
                "url": "https://${parameters.endpoint}/v1/chat/completions"
              }
            ]
          }
        },
        {
          "id": "workflow_step_2",
          "type": "register_model",
          "previous_node_inputs": {
            "workflow_step_1": "connector_id"
          },
          "user_inputs": {
            "name": "openAI-gpt-3.5-turbo",
            "function_name": "remote",
            "description": "test model"
          }
        }
      ],
      "edges": [
        {
          "source": "workflow_step_1",
          "dest": "workflow_step_2"
        }
      ]
    }
  }
}

[joshpalis]

Closed by #273