How to add Metered billing by usage with Stripe to your app?

Metered billing with Stripe means customers are charged based on how much they actually use, instead of paying a flat fee. For example, imagine a cloud storage service that charges $0.10 per gigabyte each month—if a customer uses 50 GB, they pay $5, but if they use 200 GB, they pay $20. Stripe automatically tracks usage, calculates the charges, and bills customers accurately at the end of the billing period. This way, businesses can scale pricing fairly while customers only pay for what they use.

Add usage-based billing with Stripe metered billing.

Requirements:
– Backend: create subscription with metered plan.
– Track usage events (e.g., API calls) and report to Stripe's usage API.
– Supabase table `usage (id, user_id, event, count, created_at)`.
– Admin dashboard showing current usage + bill estimate.
– Output: full integration with Stripe metered billing.