Custom Promethues exporter for subquery Observability stack

[ayshvm]

Prerequisites

• I checked the documentation and made sure this feature does not already exist.
• I checked the existing issues to make sure this feature has not already been requested.
• I have read the code of conduct before creating this issue.

Problem

we have initial metrics in place for subquery to monitor testnet and mainnet sync , db sizes, accounts and transactions via ticket: #76

• The metrcis are good to have but cant be used to apply logical operators like rate to see change in rate of sync over time and also limits the data points to 500 so we can only see data for last 2-3 days.
• need to have better visualization of these metrics to make infer from them easily.

Feature / Solution Acceptance Criteria

• created python script to act as prom exporter and send metrics directly to grafana
• plot metrcis for height, transactions , db size etc
• deploy more metrics with rate of change and others as required.

Alternatives

No response

Additional Context

No response