chore(sample): add note about secret needing to be pre-created

[gregsheremeta]

Description of your changes:
these samples currently only work on the Google Cloud distribution because of hardcoded secret name that only pre-exists there.
1 extract the hardcoded secret name to a const to make it a little easier to change
2 add a note about it.

Checklist:

• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[google-oss-prow]

Hi @gregsheremeta. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[connor-mccarthy]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: connor-mccarthy

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• samples/OWNERS [connor-mccarthy]

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[google-oss-prow]

@gregsheremeta: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
kubeflow-pipelines-samples-v2	d0cf525	link	false	/test kubeflow-pipelines-samples-v2

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.

[gregsheremeta]

thanks @connor-mccarthy . Can you re-tag? I had to add the signed-off-by.

[rimolive]

/lgtm