Rust sample app

[optout21]

Description

Sample application in Rust language.

How to test

• build and run sample app, according to the README.md.
• Check that sample is executed in the 'sample app' CI

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• [x] Create pull request as draft initially, unless its complete.
• [x] Add tests to cover changes as needed.
• [x] Update documentation as needed.
• [x] If there is a related Issue, mention it in the description.

If you're adding a new blockchain

• [ ] I have read the guidelines for adding a new blockchain.