feat: create a Rust sample for block request with particular URL/header plugin

[walves-cit]

This plugin is a block request with particular URL/header showcase.

Technically, this is performed checking if the client's referer matches an expected domain. If there's a mismatch, a 403 Forbidden error is returned.

This examples contains only a Rust version.

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• plugins/samples/block_request/plugin.rs:15, tag serviceextensions_plugin_block_request

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