fix(ui): Disable GKE Metadata as default Fixes: #11247, fixes #11260

[dvcanton]

Description of your changes:

• UI presents errors when deployed outside GKE as pointed in [frontend] Error on Kubeflow Pipelines Dashboard: 'No Healthy Upstream', '503 UC upstream_reset_before_response_started{connection_termination}' #11260.
• DISABLE_GKE_METADATA was set true as default and patched for GKE environments
• Tests were also adjusted

Fixes: #11247 & #11260

Duplicated from #11321 to include tests.

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[google-oss-prow]

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[google-oss-prow]

Hi @dvcanton. Thanks for your PR.

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