SDK - Separated the generated api client package

[Ark-kun]

Separating the generated API client brings many benefits.

• It's much easier to build the main package - No need to install Java, download swagger-generator, and run the script that cobbles together a package in style of Frankenstein's monster.
• No you can just run python setup.py sdist to build or python setup.py install to install the package
• This change is required for automatic API documentation generation services that need a package source in easy to install/use form
• This change also simplifies the Client code: Instead of having 5 separate but identical configuration classes and 5 separate but identical API client classes it now only has 1.

This change is 

[Ark-kun]

/test kubeflow-pipeline-e2e-test

[Ark-kun]

/test kubeflow-pipeline-sample-test

[kevinbache]

This is a fairly fundamental set of changes. Do you have any tests to prove that they don't break any functionality? Also, where are the changes to the swagger client generation?

[Ark-kun]

Also, where are the changes to the swagger client generation?

Here they are: https://github.com/kubeflow/pipelines/blob/dfca0f208ee5cdfa27ae97e44b1c653a4ef65988/sdk/python/build_kfp_server_api_package.sh

[kevinbache]

Good start

[kevinbache]

/lgtm pending == -> >= in the setup.py script

[kevinbache]

/lgtm; package version update note needs to go into the release playbook

[kevinbache]

/lgtm

[Ark-kun]

package version update note needs to go into the release playbook

Sure. I'll add it.

[Ark-kun]

/approve

[IronPan]

can this be put in sdk/ folder? backend/api is intend to be language agnostic. all language specific clients are currently located in the client folder.

[Ark-kun]

That's where I put it initially...

[IronPan]

/lgtm

[IronPan]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Ark-kun, IronPan

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[gaoning777]

How often is the api sdk released? is it going to be the same as the pipeline release?
If so, Could we build the api sdk in the sample test to make sure samples work for the current SDK?