Add CSV output format

[maksimov]

Add --format csv output option for easy import into spreadsheets and BI tools.

Columns: instance_id, name, source, region, instance_type, gpu_model, gpu_count, state, monthly_cost, estimated_savings, severity, signal_type, recommendation

Implementation:

• Add a FormatCSV function in internal/output/
• Use encoding/csv from stdlib
• Add "csv" case to the format switch in cmd/gpuaudit/main.go

[sospeter-57]

I'd like to work on this, could you assign it to me?

[maksimov]

Hey, thanks for your interest. Feel free to self-assign and work on it.