Enhance metrics

[srijan-27]

• A new counter metric needs to be added which represents server errors (app_server_error)
• A new counter metric for circuit open counts (app_circuit_open_count)
• Add hostname and database labels in app_sql_stats and app_mongo_stats metrics
• Add hostname in app_redis_stats metric
• Add consumer_group label in pubsub metrics

[illenko]

I may take it.

[srijan-27]

@illenko - Sure, assigning this to you.