Upgrade serde_yaml

[CeerDecy]

What this PR does / why we need it:

the package yaml-rust seems unmaintained, and the serde_yaml v0.8.26 depends on it, so upgrade the serde_yaml version to 0.9.
The new version of serde_yaml no longer supports the syntax standard: {} to automatically inject default values for enum types, need to add singleton_map annotations in discovery-handlers/opcua/src/discovery_handler.rs Line 55. references serde_yaml issue

closes #693

Special notes for your reviewer:

If applicable:

• this PR has an associated PR with documentation in akri-docs
• this PR contains unit tests
• added code adheres to standard Rust formatting (cargo fmt)
• code builds properly (cargo build)
• code is free of common mistakes (cargo clippy)
• all Akri tests succeed (cargo test)
• inline documentation builds (cargo doc)
• all commits pass the DCO bot check by being signed off -- see the failing DCO check for instructions on how to retroactively sign commits

[diconico07]

The update looks good to me, can you rebase on latest please.

My only concern is with serde_yaml now being unmaintained, but this can be solved another day, let's first get it to latest.

[CeerDecy]

@diconico07

Done!

I’m very excited to contribute to akri

[kate-goldenring]

Thanks @CeerDecy!