[Test proxy] Automate initial recording migration #43205
Description
Today, new libraries need to have their recordings manually pushed to the assets repo in order to generate an assets.json file. Instead of making library owners do this, since it's confusing and has caused issues in the past, we should automate this so that recordings are pushed if an assets.json file isn't present.
A potential issue with this would be permission-related, since manual recording migration requires some setup, but this configuration could just be specified as a basic requirement for testing.