avoid allocations

tested via
```
$ go test -benchmem -benchtime=5s -bench=Benchmark ./internal/metrics/
```

before:
```
BenchmarkPrometheusCounter-10           856818336                6.875 ns/op           0 B/op          0 allocs/op
BenchmarkOTELCounter-10                 146044255               40.92 ns/op           32 B/op          2 allocs/op
```

after:
``
BenchmarkPrometheusCounter-10           855046669                6.924 ns/op           0 B/op          0 allocs/op
BenchmarkOTELCounter-10                 293330721               21.05 ns/op           16 B/op          1 allocs/op
```

Signed-off-by: Yuri Shkuro <[email protected]>

internal/metrics/otelmetrics/factory.go

@@ -1,9 +1,13 @@
 package otelmetrics
 
 import (
-	"github.com/jaegertracing/jaeger/pkg/metrics"
+	"context"
+
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+
+	"github.com/jaegertracing/jaeger/pkg/metrics"
 )
 
 type otelFactory struct{}
@@ -26,8 +30,9 @@ func (f *otelFactory) Counter(opts metrics.Options) metrics.Counter {
 	attributeSet := attribute.NewSet(attributes...)
 
 	return &otelCounter{
-		counter:      counter,
-		attributeSet: attributeSet,
+		counter:  counter,
+		fixedCtx: context.Background(),
+		option:   metric.WithAttributeSet(attributeSet),
 	}
 }
 

internal/metrics/otelmetrics/otelCounter.go

@@ -3,15 +3,15 @@ package otelmetrics
 import (
 	"context"
 
-	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/metric"
 )
 
 type otelCounter struct {
-	counter      metric.Int64Counter
-	attributeSet attribute.Set
+	counter  metric.Int64Counter
+	fixedCtx context.Context
+	option   metric.AddOption
 }
 
 func (c *otelCounter) Inc(value int64) {
-	c.counter.Add(context.Background(), value, metric.WithAttributeSet(c.attributeSet))
+	c.counter.Add(c.fixedCtx, value, c.option)
 }