Don't expect Contet-Type header to exactly match application/json

InfluxDB seems to always include some other metadata in the `Content-Type`
header separated by semicolons like `application/json; charset=utf-8`,
and comparing the whole string with `application/json` will always fail,
resulting in almost always useless warnings without any helpful information
for the user what actually went wrong.

Author: yhabteab

lib/perfdata/influxdbcommonwriter.cpp

@@ -497,7 +497,7 @@ void InfluxdbCommonWriter::FlushWQ()
 			<< "Unexpected response code: " << response.result();
 
 		auto& contentType (response[http::field::content_type]);
-		if (contentType != "application/json") {
+		if (contentType != "application/json" && contentType != "application/json; charset=utf-8") {
 			Log(LogWarning, GetReflectionType()->GetName())
 				<< "Unexpected Content-Type: " << contentType;
 			return;
@@ -517,7 +517,7 @@ void InfluxdbCommonWriter::FlushWQ()
 		String error = jsonResponse->Get("error");
 
 		Log(LogCritical, GetReflectionType()->GetName())
-			<< "InfluxDB error message:\n" << error;
+			<< "InfluxDB error message: " << error << " :\n" << body;
 	}
 }