[Feature request] Enhanced information related to WAL archiving

The new `ObjectStore` CRD status that the barman cloud plugin introduces has taken over some of the backup-related information from the `Cluster` spec:
* the first recoverability point
* the last successful backup
* the last failed backup
They are all set together in this struct called RecoverabilityWindow, but in truth, for a continuous backup, these are not exactly the limits of the recoverability window, because on top of the last successful backup there can be wal files that essentially extend it.
Therefore i think this information would be more valuable if it also shows information about the last archived WAL file (or the last archived WAL file that was streamed up into the object store being modeled by this CRD).

I noticed in the last release this PR https://github.com/cloudnative-pg/cloudnative-pg/pull/8780 shows more complete information about the WAL, i think including that in the `ObjectStore` status can be a good addition. It would allow more programatic access to this data instead of needing to use the `kubectl cnpg status` command separately or look into the prometheus metrics.

This is of course assuming this plugin is also used for WAL archiving, but as far as i’ve seen it is the only recommended option.

まず ObjectStore CRD の status と、issue に記載されている RecoverabilityWindow フィールドを確認し、次に PR #8780 で追加された WAL 情報と比較します。kubectl cnpg status と Prometheus メトリクスが現在このデータをどのように取得しているかを確認してください。ObjectStore の status から、プログラムによるアクセスに必要な最新のアーカイブ済み WAL 情報を取得できれば完了です。

索引モデルが issue の本文から書いたものです。