fix(ui): request task logs only if pod was created

[ntny]

Description of your changes:

Request the task logs only if the pod was created and the pod name is available.

Scenario: a new task in run is about to start

1. Execution record in mlmd was created with a status of Running (in the -system-container-driver- Pod)
2. -system-container-impl- pod has not yet been started and Launcher has not yet saved the pod name into the MLMD execution
3. At this point, the Run Details/Logs tab starts pulling logs and may request them before the pod name is available, leading to an error (see attached), which could confuse the user

This issue is resolved by not requesting the log if the pod name is still unavailable. Instead of the error, the user will see an empty console until the pod is created

[google-oss-prow]

Hi @ntny. 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.

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[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[hbelmiro]

/lgtm
/ok-to-test

[hbelmiro]

cc @HumairAK

[DharmitD]

/lgtm