We currently run (on Prefect 1) our flows in a custom docker container based off of the prefect image. The image lives in our gitlab container registry. Our codebase, data input and output directories are all exposed to the container as volumes. It seems like the recommended way to achieve this in Prefect 2 is documented here. I'm curious if this is correct route and if so what exactly would be stored in blocks? Why is block storage required?