Serialize ValidationRules and Error when output format is Yaml or Json

[jpescalona]

Description: Errors are not printed when ouput is JSON or YAML format.

Steps to reproduce:

• Create an alert rule file with failures (argocd-example.yaml.txt)
• Use example/validation.yaml config file provided in project repository in examples folder.
• Execute promruval with --output argument with yaml or json

$ ./promruval validate --config-file=$(pwd)/examples/validation.yaml /tmp/rules/argocd.yaml --output json > /tmp/output.json
INFO[2024-12-03T14:06:11+01:00] processing file                               file/tmp/rules/argocd.yaml progress=1/1
INFO[2024-12-03T14:06:11+01:00] successfully dumped cache to file             file_name=.promruval_cache.json
INFO[2024-12-03T14:06:11+01:00] cache dumped                                  duration="246.631µs"
$ ./promruval validate --config-file=$(pwd)/examples/validation.yaml /tmp/rules/argocd.yaml --output yaml > /tmp/output.yaml
INFO[2024-12-03T14:06:16+01:00] processing file                               file=/tmp/rules/argocd.yaml progress=1/1
INFO[2024-12-03T14:06:16+01:00] successfully dumped cache to file             file_name=.promruval_cache.json
INFO[2024-12-03T14:06:16+01:00] cache dumped                                  duration="313.77µs"

Current results:
Output on YAML or JSON format does not contain Error values, see attached output files:

• JSON: output.json
• YAML:
  output.txt

Expected results:
Output of YAML and JSON format contain Error values, see attached files:

• JSON:
  output_ok.json

• YAML:
  output_ok.yaml.txt

Which operating system are you using? Linux Fedora 41 6.11.10-300.fc41.x86_64

go version go1.23.3 linux/amd64

Additional details:

After some research, it seems JSON or YAML Marshal does not work for Error struct: golang/go#5161

[jpescalona]

Please, feel free to provide feedback about the code, given i'm newbie on golang :)