[DOCS] Update Custom Validator Example

[Marcel-TO]

Documentation Issue Type

• Typo or grammatical error
• Incorrect or outdated information
• Unclear explanation or confusing content
• Missing documentation for a topic
• Broken links or images
• Code example not working
• Other (please describe)

Location

Page/File: content/docs/en/guides/plugin/creating-commands.mdx

Section: "Argument Validators"

Current Content

The current example of the custom validator logic seems to be outdated. It uses a different ValidationResult class and does not adhere to the builtin Validator classes.

Linked PRs

• GH-428: Fix custom validators section on the command creation guide #429
• GH-428: Fix custom validators section on the command creation guide #429