Rename options named tracing that do logging

Googlers can see: go/cloud-cxx:s-slash-tracing-logging-options

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I say we adopt OpenTelemetry’s naming scheme for our telemetry interfaces. This basically means s/Tracing/Logging/ for these types.

We will introduce new types using “Logging” instead of “Tracing”. We will leave using declarations for the old types, for backwards compatibility. We will also mark the old types as deprecated.

This looks like:
- introducing `g::c::LoggingComponentsOption`, to replace `g::c::TracingComponentsOption`.
- introducing `g::c::LoggingFormat`, to replace g::c::TracingOptions.
- introducing `g::c::LoggingFormatOption`, (in common) to replace `g::c::GrpcTracingOptionsOption` and `g::c::RestTracingOptionsOption`.
- introducing `GOOGLE_CLOUD_CPP_ENABLE_LOGGING`, `GOOGLE_CLOUD_CPP_LOGGING_FORMAT` to replace the old ones. We still respect the legacy environment variables for backwards compatibility, but we purge our docs of them.

We will need to do a pass on the public docs referencing the old types / old env vars.

We also need to look into legacy GCS env var: `CLOUD_STORAGE_TRACING`

まず、公開 API 宣言とドキュメントで、一覧にある Tracing 型、環境変数、レガシー名 CLOUD_STORAGE_TRACING を検索します。名前変更を計画する前に各参照を追跡し、その後、新しい Logging 名がドキュメント化されている一方で、レガシー名と変数が指定どおり引き続きサポートされ、非推奨になっていることを確認します。

索引モデルが issue の本文から書いたものです。