Feature: Add metrics to show count of processed, submitted, failed tasks into dashboard

[vikash1807]

• Create a store/metrics.py - introduce methods to increment the count of all submited, failed, processed, retries and dead letter tasks, and reads Metrics and EnhancedMetrics.
• Expose two endpoints -
  1. GET("api/metrics") to get the metric info.
  2. GET("api/metrics/enhanced") - includes extra information(e.g. - queue_size, delayd_queue_size, success_rate)
• Create a separate MetricService class in services.py.
• Update worker/executor.py and services/task.py to count the metrics variables.