Make YAML the default format for Vector

[pront]

Important

We are still supporting TOML and JSON.

Parent ticket to track related work.

Tasks

Beta Give feedback

1. Make yaml the default choice for example configurations.
2. Do a pass over all docs and replace examples using .toml with .yaml.
3. Add a format argument to the generate command and generate yaml configurations by default.
4. Add fallback for /etc/vector/vector.yaml.
5. Write a highlight for the next release.
6. Deprecate defaut location /etc/vector/vector.toml
7. After Vector 0.35.0 is released, we can remove the special code for handling /etc/vector/vector.toml