chore(front-matter_linter): migrate to yargs from @caporal/core

[caugner]

Description

Migrates scripts/front-matter_linter from @caporal/core to yargs, and removes @caporal/core from dependencies.

Motivation

@caporal/core is no longer maintained, and we already use yargs elsewhere.

Additional details

Eliminates 3 low severity vulnerabilities reported by npm install / npm audit:

// Before
26 vulnerabilities (5 low, 3 moderate, 18 high)
 
// After
23 vulnerabilities (2 low, 3 moderate, 18 high)

Related issues and pull requests

Part of mdn/fred#1121.