Add a class that validates whether the keys required by the application exist in the current environment

[MrDave1999]

The idea of this new feature is to be able to request that certain keys are required by the application, in case they do not exist in the current environment, an error is generated.

Example:

new EnvLoader().Load();
new EnvValidator()
       .SetRequiredKeys("SERVICE_APP_ID", "SERVICE_KEY", "SERVICE_SECRET")
       .Validate();

In the above example we first load the .env file and set the variables, then we call the Validate method to validate if the required keys exist in the current environment, otherwise an exception is thrown.

In other words, after calling the Load method, it will check if the keys "SERVICE_APP_ID", "SERVICE_KEY", "SERVICE_SECRET" exist in the environment of the current process.

You can also ignore the exception and handle the error in another way:

new EnvLoader().Load();
new EnvValidator()
       .IgnoreException()
       .SetRequiredKeys("SERVICE_APP_ID", "SERVICE_KEY", "SERVICE_SECRET")
       .Validate(out EnvValidationResult result);

Console.WriteLine(result.ErrorMessages);

You can also represent the required keys in a class and use each property as a key, for example:

class RequiredKeys
{
    public string SERVICE_APP_ID { get; }
    public string SERVICE_KEY { get; }
    public string SERVICE_SECRET { get; }
}

new EnvLoader().Load();
new EnvValidator()
       .IgnoreException()
       .SetRequiredKeys<RequiredKeys>()
       .Validate(out EnvValidationResult result);

Console.WriteLine(result.ErrorMessages);