feat(go-client): Introduced Prometheus for go-client monitoring and added multiple metric collection sites

[nanorth]

What problem does this PR solve?

This PR introduces Prometheus for go-client monitoring, and adds multiple metric collection points to enhance observability of the system.

What is changed and how does it work?

This PR integrates the Prometheus client libraries (github.com/prometheus/client_golang and github.com/prometheus/client_model) as tools for metric instrumentation and data reporting.

Checklist

Tests

• Manual test (add detailed scripts or steps below)
  Use go-client to invoke several interfaces, and the metrics were verified to be correctly reported on Prometheus monitoring services.

Code changes

• Has exported function/method change
  Added metric collection for operation counts and latencies in func (p *pegasusTableConnector) runPartitionOp.
  Added RPC request size metric collection in func (n *nodeSession) writeRequest.
• Has exported variable/fields change
  Added a new field enablePerfCounter in nodeSession to distinguish between meta and replica nodes. Performance metrics are collected only for replica nodes. The constructor has been updated accordingly.
• Package structure change
  The Config struct has been moved into a separate package to avoid circular dependencies.

Related changes

• Need to update the documentation
  Since the Config struct has been moved to a separate package, the example code has also been updated to reflect this change.

[Copilot]

Pull Request Overview

This PR integrates Prometheus monitoring into the go-client by adding metric collection capabilities and refactoring the configuration structure to support observability features.

• Adds Prometheus client libraries for metrics collection including operation counts, latencies, and RPC message sizes
• Refactors configuration by moving the Config struct to a separate package to avoid circular dependencies
• Introduces metrics collection at multiple points in the client execution flow

Reviewed Changes

Copilot reviewed 21 out of 22 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
go-client/session/session_test.go	Updates test cases to include the new enableMetrics parameter in session constructors
go-client/session/session.go	Adds metrics collection for RPC message sizes and updates function signatures to support metrics configuration
go-client/session/replica_session.go	Updates replica manager to support metrics configuration through constructor parameters
go-client/session/meta_session.go	Adds getter method for meta IP addresses and updates session creation to disable metrics for meta nodes
go-client/session/meta_call.go	Updates meta session creation to disable metrics for new meta nodes
go-client/pegasus/table_connector_test.go	Updates import and config usage to reference the new config package
go-client/pegasus/table_connector.go	Adds comprehensive metrics collection for operation counts and latencies with detailed labeling
go-client/pegasus/config.go	Removes the original Config struct (moved to separate package)
go-client/pegasus/client_test.go	Updates all test cases to use the new config package
go-client/pegasus/client.go	Integrates Prometheus initialization and updates client creation to support metrics configuration
go-client/metrics/prometheus_test.go	Adds unit tests for concurrent metrics operations and singleton behavior
go-client/metrics/prometheus.go	Implements the core Prometheus metrics functionality with thread-safe metric creation and collection
go-client/integration/failover-test/main.go	Updates import to use the new config package
go-client/go.mod	Adds Prometheus client dependencies and updates related package versions
go-client/example/pegasus-client-config.json	Adds Prometheus configuration options to the example configuration
go-client/example/main.go	Updates import to use the new config package
go-client/example/full_scan.md	Updates documentation example to use the new config package
go-client/config/config.go	Introduces the new configuration package with Prometheus support and option pattern
go-client/admin/remote_cmd_client.go	Updates session creation to disable metrics for admin operations
go-client/admin/client_test.go	Updates import to use the new config package
go-client/admin/client.go	Fixes struct formatting in create table request

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[acelyc111]

@nanorth Thanks for the contribution!