Unable to set filter for BetterStackLoggerProvider

[Jericho]

Microsoft.Extensions.Logging provides the following method: AddFilter<T>(...) where T : ILoggerProvider which allows developers to configure the logging level for a specific logging provider. For example, in the following code snippet I have configured the default log level to Debug and I was able to override this log level for the console to Information:

logging.AddFilter(logLevel => logLevel >= LogLevel.Debug);
logging.AddFilter<ConsoleLoggerProvider>(logLevel => logLevel >= LogLevel.Information);

Unfortunately I am unable to do the same for BetterStackLoggerProvider because this class is marked as internal. If this class was marked as public I would be able to write code like this:

logging.AddFilter<BetterStackLoggerProvider>(logLevel => logLevel >= LogLevel.Error);

I propose marking the BetterStackLoggerProvider as public and I will be happy to submit a PR.