docs(client_libs): update code examples for v3 client to new Point API

[bednar]

Updated code examples for v3 clients to new unified Point API. For more info see changes in releases notes:

• C# - 0.3.0 - https://github.com/influxcommunity/influxdb3-csharp/blob/main/CHANGELOG.md#030-2023-10-02
• Js/NodeJS - 0.3.0 - https://github.com/influxcommunity/influxdb3-js/blob/main/CHANGELOG.md#030-2023-10-02

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[appletreeisyellow]

Sorry it took so long to review it! Thanks for keeping it updated