[Backend] Cases list and count routes should return info from the 'data' folder

[amlannandy]

Describe the bug Currently, the cases list and count routes are trying to fetch data using the Case SQL Model which hasn't been setup yet. We can change it directly fetch the cases from the data folder, similar to how open-case and open-folder routes are working.

To Reproduce Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior A clear and concise description of what you expected to happen.

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context I'll soon submit a PR for it.