Ephemeral container expiration improvements

[pditommaso]

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Ephemeral containers are accessible for a fixed period of time (a few hours) since their request.

However there are use cases (e.g. long workflow runs) that may require to be able to access such container for a longer period of time.

This PR extends the current logic so that when a container is requested by a workflow run submitted via Platform the container expiration time is extended as long as the corresponding workflow execution is running.

[munishchouhan]

@pditommaso Can we move forward with this PR? or is it blocked by some other changes?