Don't keep unused containers in Blob Storage

[celticr]

Originally created by @boolean5 on 2024-06-12T07:35:12Z
Original issue: SpringACT/digital-safe-upload-on-blob#562

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During the Digital Safe creation process, if the user clicks on "Previous" after having created the image password, the newly created container that corresponds to the key in this image is never used but also never deleted from the Blob Storage.

Two approaches to consider:

1. When clicking on "Previous" at this step, let's issue a request to delete the newly created container for the key stored in the previous image to avoid piling up unused containers in our Blob Storage. Check if a similar thing is also needed for other steps (e.g. entering the Digital Safe name).
2. Only create the container in the Blob Storage when the user clicks on the final "Next" button in the creation process (i.e., after having created the image password, after downloading it and after clicking "Next")