Set temporary expiration date for versioned vector stores

[SmittieC]

When we create a vector store during versioning and something goes wrong, the new experiment version gets rolled back. However, we do not do any sort of cleanup of the potentially created vector store on OpenAI. This could potentially create an expensive artefact.

A potential fix:
We set an expiration date when creating the vector store the first time during versioning. Only after the version was created successfully do we go back and remove that expiration date so that this version will not lose its vector store.

[SmittieC]

cc @snopoke