feat: create a Rust sample plugin for overwriting error codes from 5XX to 4XX classes.

[pweiber]

Rust version for the overwriting error codes.

This is performed by replacing the 5XX error code response to 4XX.

[snippet-bot]

Here is the summary of changes.

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• plugins/samples/overwrite_errcode/plugin.rs:15, tag serviceextensions_plugin_overwrite_errcode

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