WIP - chore(backend): remove bazel from backend code generation

[Bobgy]

Description of your changes:
This is my attempt forking from #4906.

Run the following to generate

# cd backend/api
docker build ../.. -t builder -f ../Dockerfile.buildapi
./generate_api.sh

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[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Bobgy

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Bobgy

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• OWNERS [Bobgy]

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[Bobgy]

/cc @NikeNano
I put up a working version

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[NikeNano]

How do we generally do with updating licenses?

[Bobgy]

We usually update the date to include the last year there's a change, so we should update this as
Copyright 2020-2021 The Kubeflow Authors, because you created it.

[google-oss-robot]

@Bobgy: The following tests failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
kubeflow-pipeline-backend-test	1e7a338	link	/test kubeflow-pipeline-backend-test
kubeflow-pipeline-sample-test	1e7a338	link	/test kubeflow-pipeline-sample-test
kubeflow-pipeline-upgrade-test	1e7a338	link	/test kubeflow-pipeline-upgrade-test
kubeflow-pipeline-e2e-test	1e7a338	link	/test kubeflow-pipeline-e2e-test
kubeflow-pipeline-frontend-test	1e7a338	link	/test kubeflow-pipeline-frontend-test

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

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