Add property BetterStackLogsTarget.IncludeScopeContext

[menuet]

Hi
Currently, the target BetterStackLogsTarget uploads only the GlobalDiagnosticContext's properties.
It is useful for us to uplaod the ScopeContext's properties too.
So we duplicated and hacked your class in our code base for this purpose.
We made this PR in case you are interested to make this patch available to everyone (and for getting rid of our duplicate if yours does the job).
Regards

[snakefoot]

Notice that you inherit from TargetWithContext, which correctly handles ScopeContext. Where you can call

{
   IDictionary<string,object> logProperties = this.GetAllProperties(logEvent);
}

See also: https://github.com/NLog/NLog/wiki/How-to-write-a-custom-target-for-structured-logging

Maybe this will be better:

        protected override void Write(LogEventInfo logEvent)
        {
            var properties = GetAllProperties(logEvent); // Assign IncludeEventProperties = true in constructor

            var contextDictionary = new Dictionary<string, object> {
                ["logger"] = logEvent.LoggerName,
                ["properties"] = properties,
                ["runtime"] = new Dictionary<string, object> {
                    ["class"] = logEvent.CallerClassName,
                    ["member"] = logEvent.CallerMemberName,
                    ["file"] = string.IsNullOrEmpty(logEvent.CallerFilePath) ? null : logEvent.CallerFilePath,
                    ["line"] = string.IsNullOrEmpty(logEvent.CallerFilePath) ? null : logEvent.CallerLineNumber as int?,
                },
            };

[snakefoot]

Acronyms like "sc" are not easy for others to understand

[snakefoot]

NLog TargetWithContext already provides IncludeScopeProperties that works together with GetAllProperties()

[snakefoot]

Created #7 that uses NLog JsonLayout for output of ScopeContext-properties. By specifying IncludeScopeProperties = true