style: format code with Gofumpt and Prettier

This commit fixes the style issues introduced in c6e1311 according to the output
from Gofumpt and Prettier.

Details: #2161

internal/observability/metrics/mem/mem.go

@@ -1,18 +1,16 @@
-//
 // Copyright (C) 2019-2023 vdaas.org vald team <[email protected]>
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // You may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//    https://www.apache.org/licenses/LICENSE-2.0
+//	https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-//
 package mem
 
 import (

internal/observability/observability.go

@@ -1,18 +1,16 @@
-//
 // Copyright (C) 2019-2023 vdaas.org vald team <[email protected]>
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // You may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//    https://www.apache.org/licenses/LICENSE-2.0
+//	https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-//
 package observability
 
 import (