Rust: add invoke-agent example in bedrock-agent-runtime

[mattiapitossi]

Hi there,

This pull request adds an example to use the invoke agent command in Rust:

• Add bedrock-agent-runtime invoke-agent example
• Example is based on the jsv3

Let me know if it makes sense for you.

Thanks!

command:

cargo run --bin invoke-agent

closes #7480

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