feat: create a rust sample plugin for JWT authorization.

[pweiber]

This plugin is a JWT authorization showcase.

Technically, this is performed by ensuring that the request query string has a valid signed JWT. If it is valid it will be removed from the URL.

This example contains only a Rust version.

Note:
Added a new test file for the Rust version to avoid some conflicts due to the c++ log regex version, let me know if that's fine.

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• plugins/samples/jwt_auth/plugin.rs:15, tag serviceextensions_plugin_jwt_auth

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment