fix namespace config drift

[freeznet]

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Similar to hashicorp/terraform-plugin-sdk#123

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[github-actions]

@freeznet:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[langesven]

I might be mistaken but this appears to introduce a change of default values that have a different meaning than previously.

This change changes the default for offload_threshold_size_in_mb from -1 to 0.

From the 3.0.x docs

Maximum number of bytes stored in the pulsar cluster for a topic before data will start being automatically offloaded to longterm storage (eg: 10M, 16G, 3T, 100).
-1 falls back to the cluster’s namespace default.
Negative values disable automatic offload.
0 triggers offloading as soon as possible

So with this change now wanting to switch all offload_threshold_size_in_mb if not defined from -1 (disabled) to 0 (offload as soon as possible) is a 180 on previous behaviour.

The docs for 4.0.x are missing the explanation, but it's visible in the source code at least as well as the default being -1

Additionally due to validateGtEq0 being used it's not possible to still actively set a value of -1

Error: "namespace_config.0.offload_threshold_size_in_mb" must be 0 or more, got: -1