alertmanagerexporter: migrate to latest semconv version (#35341)

Description: The version of semconv is upgraded from v1.6.1 to v1.27.0

This is a trivial migration. semconv usage inside component:

- conventions.AttributeServiceName="service.name" on both versions

Link to tracking Issue:
#22095

Testing: Tests passed

exporter/alertmanagerexporter/alertmanager_exporter_test.go

@@ -22,7 +22,7 @@ import (
 	"go.opentelemetry.io/collector/exporter/exportertest"
 	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/pdata/ptrace"
-	conventions "go.opentelemetry.io/collector/semconv/v1.6.1"
+	conventions "go.opentelemetry.io/collector/semconv/v1.27.0"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/common/testutil"
 )