Replace serde_yaml

[cathay4t]

The maintainer of serde_yaml has announced the demise of that crate:
https://github.com/dtolnay/serde-yaml

We need to replace it.

[cathay4t]

Considering we never hit any problem of using serde_yaml, let's keep using it till better option shows up.

[jubril-adeyi]

Hello @cathay4t do you mind sharing what replacement options are available for serde-yaml ?
i'd like to work on this issue

[Mabwas]

@cathay4t can i work this please

[cathay4t]

Hi @jubril-adeyi @Mabwas, I don't have preference on replacement yet.
Replacing a dependency need to answer these questions with proofs:

1. Is the new crate API stable enough?
2. Is the new crate well tested by community?
3. YAML API is the key API of nmstate, no CI test failure should caused by this change.

Personally, unless deprecated serde-yaml proved to be holding unfixed bugs, I would like to keep using it.

So, it might not be a good task for new contributor.

If you like to accept the challenge, PR is always welcome once you have proofs on above questions.

[ihuguet]

I also think that keeping serde_yaml is the best choice, for the moment. However, this seems a potential good replacement (which is a continuation of serde_yaml): https://crates.io/crates/serde_yaml_ng