`az ml pipeline list` does not return pipeline attributes

### Extension name (the extension in question)

ml

### Description of issue (in as much detail as possible)

Output of `az ml pipeline list` is messed up as it mixes fixed strings "Pipeline:" and objects into a single array. Also most of the pipeline attributes (Version, Tags etc.) are missing, although they are returned by the underlying call to 'https://westus2.aether.ms/api/v1.0/subscriptions/a4ed7b9a-b128-49b4-a6ee-fd07ff6e296d/resourceGroups/rg-myappdataops-test-main/providers/Microsoft.MachineLearningServices/workspaces/aml-myappdataops-test/Pipelines?activeOnly=true'.

```
az ml pipeline list
[
"Pipeline:",
{
"Endpoint": "https://westus2.aether.ms/api/v1.0/subscriptions/a4ed7b9a-b128-49b4-a6ee-fd07ff6e296d/resourceGroups/rg-myappdataops-test-main/providers/Microsoft.MachineLearningServices/workspaces/aml-myappdataops-test/PipelineRuns/PipelineSubmit/fa809332-6d2d-4336-8951-fcdcc3c0fb92",
"Id": "fa809332-6d2d-4336-8951-fcdcc3c0fb92",
"Name": "Feature Engineering",
"Status": "Active"
},
"Pipeline:",
{
"Endpoint": "https://westus2.aether.ms/api/v1.0/subscriptions/a4ed7b9a-b128-49b4-a6ee-fd07ff6e296d/resourceGroups/rg-myappdataops-test-main/providers/Microsoft.MachineLearningServices/workspaces/aml-myappdataops-test/PipelineRuns/PipelineSubmit/6c83079d-923a-4fee-bbb7-46f9f3f4426c",
"Id": "6c83079d-923a-4fee-bbb7-46f9f3f4426c",
"Name": "Feature Engineering",
"Status": "Active"
},
"Pipeline:",
```

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