Retrieves a URL string from an environment variable, validates it, and ensures it doesn't end with a trailing slash.
The name of the environment variable
Optional
Optional default URL string to use if the environment variable is not set
The validated URL string with any trailing slash removed
Will throw an error if the URL is invalid, or if the environment variable is missing and no default is provided
Retrieves a URL string from an environment variable, validates it, and ensures it doesn't end with a trailing slash.