Virtual registry: clear upstream cache

🔥 Problem

At the time of this writing, there is no way to clear the entire cache of a given upstream or a given registry.

🚒 Solution

• Provide an API endpoint to clear the cache of an upstream.
• Provide an API endpoint to clear the cache of a registry.

⚠️ Even though cache entries can be marked for destruction (column status), doing an upstream's cache reset can translate in a very large amount of UPDATE statements.

Either:

• batch them together or
• implement the clear logic as a stateful workflow where an upstream being cleared goes through a background job that has more time to update the status columns.