fix: add additional formatter support to the validate subcommand

[sekikn]

Description

• This PR adds additional formatters to the validate subcommand in alignment with its help message.

Related issue(s)

Resolves #2007

[changeset-bot]

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Latest commit: b9bdd84

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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[abhi-03-kh]

@sekikn Tested locally on Linux/Node 20.

Verified that both formats work correctly now:

• markdown: Outputs proper Markdown table with | Code | Path | Message | columns.
• github-actions: Outputs ::error and ::warning annotations as expected.

This correctly fixes the issue where these options appeared in --help but produced the same output as the default stylish format.

[Souvikns]

@aayushmau5 do you think we need this?

[SnakeDoc]

I'm just a random user, but I'd love to see this addition. I was recently shocked to see the cli didn't support github-actions and other output formats, and stumbled upon #2007 and this PR as I was researching opening my own.

Both Spectral and Redocly support the formats @sekikn has proposed adding. I think this would be a great addition.