Add support for loading edit spec from YAML file

[IndrekHaav]

This PR adds support for loading the edit spec from a YAML file.

Specifying the filename works the same as for JSON - either implicitly as the only CLI argument (if it ends with .yml or .yaml), or explicitly with the --yaml flag.

Example:

$ cat project.yaml
---
outPath: output_yaml.gif
clips:
  - layers:
      - type: title-background
        text: YAML config

$ podman run --rm -it -v $(pwd):/videos:z -w /videos editly/editly editly project.yaml
ffmpeg version 5.1.6
ffprobe version 5.1.6
320x320 10fps
  0%  25%  50%  75% 100% Done with transition, switching to next transitionFromClip (1)
No more transitionFromClip, done

Done. Output file can be found at:
output_yaml.gif

Result: