[HbarLimitService] Replace updateAverageAmountSpentPerSubscriptionTier with Efficient Metrics Collection

[quiet-node]

Problem

The updateAverageAmountSpentPerSubscriptionTier method in HbarLimitService generates excessive logs when the database contains many HBAR spending plans. It retrieves all active plans for a subscription tier, calculates the average amount spent, and updates a Prometheus gauge.

When there are numerous accounts, this process:

• Iterates over potentially large collections of accounts
• Creates multiple database queries
• Generates excessive debug logs
• Performs calculations that could be done more efficiently at visualization time

Proposed Solution

1. Remove the updateAverageAmountSpentPerSubscriptionTier method entirely
2. Replace with two separate metrics:
   • Track the total amount spent per subscription tier
   • Track the count of active plans per subscription tier (already implemented)
3. Leverage Grafana's calculation capabilities to compute the average (total amount / count) at visualization time

Benefits

• Reduced database load: No need to frequently fetch all plans
• Decreased log volume: Elimination of unnecessary log entries for each calculation
• More efficient metrics collection: Basic counters instead of complex calculations
• Improved performance: Calculations moved to visualization layer (Grafana)
• Better scalability: Solution works efficiently regardless of the number of accounts

Implementation Notes

• The current averageSpendingPlanAmountSpentGauge should be replaced with a new gauge for tracking total amount spent
• Existing counters for tracking unique plans can be utilized for the denominator
• Transition should be seamless for monitoring dashboards with proper Grafana query adjustments