[core] Expose Redis getter to Python and use to retrieve session name

[vitsai]

… (#39194)

If only GCS communicates with Redis, there is no way to initialize the log directories using persisted values. However, these directories are required to exist before starting GCS. Expose a function to the Python layer specifically to retrieve these keys from Redis and set them. Follow-ups will ensure that these keys are only set and retrieved through this interface.

Why are these changes needed?

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[GeneDer]

@vitsai to fix DCO :)

[vitsai]

Sorry, done

[zhe-thoughts]

Yes this is a release blocker to pick