The URL to validate
True if the URL is valid and uses HTTPS (or HTTP for localhost)
isValidWellknownUrl('https://am.example.com/.well-known/openid-configuration')
// Returns: true
isValidWellknownUrl('http://localhost:8080/.well-known/openid-configuration')
// Returns: true (localhost allows HTTP)
isValidWellknownUrl('http://am.example.com/.well-known/openid-configuration')
// Returns: false (non-localhost requires HTTPS)
isValidWellknownUrl('not-a-url')
// Returns: false
Validates that a well-known URL is properly formatted.