Support optional BasicAuthentication for plugin Maven repositories

[shanerbaner82]

Summary

• Adds support for an optional "authentication": "basic" field in plugin nativephp.json repository configuration
• When declared, the compiler generates the required authentication { create<BasicAuthentication>("basic") } block in settings.gradle.kts
• This is required by Maven repositories like Mapbox Navigation SDK that need preemptive Basic auth for credential-based access

Plugin manifest example

"repositories": [
    {
        "url": "https://api.mapbox.com/downloads/v2/releases/maven",
        "authentication": "basic",
        "credentials": {
            "username": "mapbox",
            "password": "${MAPBOX_DOWNLOADS_TOKEN}"
        }
    }
]

Test plan

• Verified locally that settings.gradle.kts generates correct auth block when "authentication": "basic" is set
• Verified locally that existing plugins without authentication field are unaffected
• Verified Mapbox Navigation SDK resolves successfully with the auth block
• Verified bifrost CI build passes with this change