Use YAML 1.2 throughout

Use YAML 1.2 throughout

The `yes` and `no` boolean values do not exist in YAML 1.2 [1].

Change all of them for `true` and `false`.

Also, in `tests/tracing/configs` and in
`examples/linux-fs-simple/config.yaml`, add the explicit `%YAML 1.2`
directive to indicate that it's a YAML 1.2 document.

[1]: https://yaml.org/spec/1.2/spec.html#id2805071

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>