(fix) Clear user config cache for every 1000 users

Description

Screenshots

Technical details

Tests

Memory usage is significantly reduced after fix ✅

Before:

Current memory usage after 1000 users: 609.3 MB
Current memory usage after 2000 users: 1.1 GB
Current memory usage after 3000 users: 1.1 GB
Current memory usage after 4000 users: 1.1 GB
Current memory usage after 5000 users: 1.1 GB
Current memory usage after 6000 users: 1.2 GB
Current memory usage after 7000 users: 1.2 GB
Current memory usage after 8000 users: 1.2 GB

After:

Current memory usage after 1000 users: 609.5 MB
Current memory usage after clearing cache: 58.9 MB
Current memory usage after 2000 users: 550.2 MB
Current memory usage after clearing cache: 59.9 MB
Current memory usage after 3000 users: 81.3 MB
Current memory usage after clearing cache: 61.1 MB

Issues

• https://gitlab.e.foundation/e/infra/backlog/-/issues/4980+

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