Merge pull request gofr-dev#768 from gofr-dev/EN/docs-custom-metrics

Enhance custom metrics doc

Author: vikash

docs/advanced-guide/publishing-custom-metrics/page.md

@@ -64,7 +64,7 @@ func main() {
 	app.Metrics().NewUpDownCounter("total_credit_day_sale", "used to track the total credit sales in a day")
 
 	app.POST("/sale", func(ctx *gofr.Context) (interface{}, error) {
-		ctx.Metrics().IncrementCounter(ctx, "total_credit_day_sale")
+		ctx.Metrics().DeltaUpDownCounter(ctx, "total_credit_day_sale", 1000)
 
 		return "Sale Completed", nil
 	})
@@ -139,6 +139,76 @@ func main() {
 }
 ```
 
+## Adding Labels to Custom Metrics
+
+GoFr leverages metrics support by enabling labels. Labels are a key feature in metrics that allow you to categorize and filter metrics based on relevant information.
+
+### Understanding Labels
+
+Labels are key-value pairs attached to metrics. They provide additional context about the metric data.
+
+Common examples of labels include:
+- environment: (e.g., "production", "staging")
+- service: (e.g., "api-gateway", "database")
+- status: (e.g., "success", "failure")
+
+By adding labels, you can create different time series for the same metric based on the label values.
+This allows for more granular analysis and visualization in Grafana (or any other) dashboards.
+
+### Additional Considerations
+
+- Prefer to keep the number of labels manageable to avoid overwhelming complexity.
+- Choose meaningful label names that clearly describe the data point.
+- Ensure consistency in label naming conventions across your application.
+
+By effectively using labels in GoFr, you can enrich your custom metrics and gain deeper insights into your application's performance and behavior.
+
+### Usage:
+
+Labels are added while populating the data for metrics, by passing them as arguments (comma separated key-value pairs)
+in the GoFr's methods (namely: `IncreamentCounter`, `DeltaUpDownCounter`, `RecordHistogram`, `SetGauge`).
+
+Example: `c.Metrics().IncrementCounter(c, "metric-name", "metric-value", "label-1", "value-1", "label-2", "value-2")`
+
+```go
+package main
+
+import (
+	"gofr.dev/pkg/gofr"
+)
+
+func main() {
+	// Initialise gofr object
+	a := gofr.New()
+
+	// Add custom metrics
+	a.Metrics().NewUpDownCounter("total_credit_day_sale", "used to track the total credit sales in a day")
+
+	// Add all the routes
+	a.POST("/sale", SaleHandler)
+	a.POST("/return", ReturnHandler)
+
+	// Run the application
+	a.Run()
+}
+
+func SaleHandler(c *gofr.Context) (interface{}, error) {
+	// logic to create sales
+
+	c.Metrics().DeltaUpDownCounter(c, "total_credit_day_sale", 10, "sale_type", "credit", "product_type", "beverage") // Here "sale_type" & "product_type" are the labels and "credit" & "beverage" are the values
+
+	return "Sale Successful", nil
+}
+
+func ReturnHandler(c *gofr.Context) (interface{}, error) {
+	// logic to create a sales return
+
+	c.Metrics().DeltaUpDownCounter(c, "total_credit_day_sale", -5, "sale_type", "credit_return", "product_type", "dairy")
+
+	return "Return Successful", nil
+}
+```
+
 **Good To Know**
 
 ```doc