Expose an API for appending params/names/descriptions in a programmable way.

[numerology]

An effort towards #1942

Add an API kfp.compiler.Compiler.create_workflow_from_func(func, name, description, params_list)
Usage:
Create workflow spec from pipeline function and specified pipeline params/metadata.

Now we can do something like the following:

ppl_param = dsl.PipelineParam(name='arg_specified_at_runtime')

def some_op():
  '''Example containerOp'''
  return dsl.ContainerOp(
      name='some op',
      image='busybox',
      command=['sleep 1'],
      arguments=[ppl_param]
  )

def pipeline_func():
  task = some_op()

compiler.Compiler().create_workflow(
    func=pipeline_func,
    name='Example Pipeline',
    description='Example description',
    params_list=[ppl_param])

It returns the workflow spec of the pipeline, then it can be dumped to yaml spec.

---

This change is 

[numerology]

/retest

[numerology]

/test kubeflow-pipeline-sample-test

[numerology]

/retest

[numerology]

/test kubeflow-pipeline-e2e-test

[neuromage]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: neuromage

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[numerology]

/test kubeflow-pipeline-e2e-test