As a use, I want to add URI label to http_requests_total metric in prometheus plugin

[evle]

Description

The current prometheus plugin provides http_requests_total metric to track the total number of client requests. However, it lacks the ability to track requests by URI, which is crucial for monitoring traffic patterns and identifying potential bottlenecks at the endpoint level.

Why

Currently, http_requests_total is defined as a simple gauge without labels:

metrics.requests = prometheus:gauge("http_requests_total"

This would allow users to:

• Track request counts per endpoint
• Set up alerts based on endpoint-specific traffic patterns
• Better understand traffic distribution across different APIs

In addition, it will be consistent with other metrics like http_status which already includes URI information

[evle]

Breaking Changes Reminder:

• Current query: apisix_http_requests_total (returns single total value)
• After adding labels: Would require sum(apisix_http_requests_total) to get the same total
• This would break existing dashboards, alerts, and monitoring setups

Proposed Solution:
Add a new metric apisix_http_route_requests_total with route labels instead of modifying the existing one. This ensures backward compatibility is maintained