sdk/metric: Fix import comments (open-telemetry#4086)

* Resolve inconsistent import comments in sdk/metric

* update changelog

* Apply suggestions from code review

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update CHANGELOG.md

---------

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Robert Pająk <pellared@hotmail.com>

Author: 4 people

sdk/metric/manual_reader_test.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package metric // import "go.opentelemetry.io/otel/sdk/metric/reader"
+package metric // import "go.opentelemetry.io/otel/sdk/metric"
 
 import (
 	"testing"

sdk/metric/reader_test.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package metric // import "go.opentelemetry.io/otel/sdk/metric/reader"
+package metric // import "go.opentelemetry.io/otel/sdk/metric"
 
 import (
 	"context"