Switch config format from toml to yaml

[mobileoverlord]

Avocado configs are simpler to scan and visually parse using yaml.
Here is a preview of what yaml configs would look like:

default_target: jetson-orin-nano-devkit
supported_targets:
- jetson-orin-nano-devkit
runtime:
  dev:
    dependencies:
      avocado-img-bootfiles: '*'
      avocado-img-rootfs: '*'
      avocado-img-initramfs: '*'
      config:
        ext: config
      app:
        ext: app
    jetson-orin-nano-devkit:
      dependencies:
        avocado-img-tegraflash: '*'
ext:
  app:
    types:
    - sysext
    - confext
    version: 0.1.0
    dependencies: {}
  config:
    types:
    - confext
    version: 0.1.0
    users:
      root:
        password: ''
sdk:
  image: docker.io/avocadolinux/sdk:apollo-edge
  dependencies:
    avocado-sdk-toolchain: '*'
  jetson-orin-nano-devkit:
    container_args:
    - --network=host
    - -v
    - /dev:/dev
    - -v
    - /sys:/sys:ro
    - --privileged
    dependencies:
      nativesdk-util-linux-mount: '*'

This PR changes the default config file format form toml to yaml. With a couple considerations

• We look for a config in the following order: avocado.yaml | avocado yml | avocado.toml. We accept using both yaml and yml extension names.
• If we encounter a toml config, automatically migrate it to avocado.yaml