Use constant for metric name instead of hardcoded string literals

[dgroup]

Summary

Key	Value
Rule	UseConstantAsMetricName
Ruleset	io/github/dgroup/arch4u/pmd/arch4u-ruleset.xml
Category	Error Prone
Framework	io.micrometer:micrometer-core
Since	0.1.0
Incidents in past at my experience	1

Why?

The monitoring metric name should be provided into annotation @Timed by constant, not a hardcoded string:

@RestController
public class MyController {
  
   @Timed(Metrics.ORDER_PROCESSING_DURATION)   // ok
   public X process(Order order) {
      ...
   }

  @Timed("order_processing_duration")    // violation
  public X process(Order order) {
     ...
   }
}

The passing of string literal leads to potential code duplications and possible errors.