[hotfix][docs] Add missing CSV and JSON entries to DataStream formats overview

[Dennis-Mircea]

What is the purpose of the change

The "Available Formats" list on the DataStream Formats overview page is missing two entries that already exist as documented formats in the same directory: csv.md and json.md. As a result, users browsing the overview cannot discover the CSV and JSON format docs from there. This pull request adds those two entries to the list, in both the English and Chinese versions of the page.

Brief change log

• docs/content/docs/connectors/datastream/formats/overview.md: add CSV and JSON entries to the "Available Formats" list, kept in alphabetical order with the existing entries.
• docs/content.zh/docs/connectors/datastream/formats/overview.md: same change applied to the Chinese mirror to keep it in sync.

The linked targets (docs/connectors/datastream/formats/csv and .../json) already exist; no new pages are added.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

[flinkbot]

CI report:

• 903bfe0 Azure: SUCCESS

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[spuru9]

LGTM. Thanks.

[raminqaf]

Thanks for adding these!