feat: Add a rust plugin to add geo query string to URL

[mateustd-ciandt]

Adding a new rust plugin in order to modulate content based on the country value.
This value is added as a query string name value pair in the URL.
The query string value is also available in the normal GCP logs.

C++ version PR: #289

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• plugins/samples/add_geo_query/plugin.rs:15, tag serviceextensions_plugin_country_query

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[mpwarres]

See comment #289 (comment) , the plugin should access geo information via the get_property() API, in anticipation of attribute support for geo info to be added in Q1.

[mpwarres]

LGTM mod comment

[mpwarres]

I think it is more idiomatic to adjust this to be:

const CLIENT_REGION_PATH: [&str] = ["request", "client_region"];

[mateustd-ciandt]

Hi Mike! I believe in Rust [&str] doesn't compile because unsized types cannot be used in const. So as far as I know, we need either &[&str] (reference to slice) or [&str; 2] (array with explicit size).