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

[mateustd-ciandt]

Adding a new GO 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
Rust version PR: #294

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

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

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