L-849 Send logs in configured batches, repeat sending unsuccessful data (#18)

* Do not sent batches larger than configured batchSize to Better Stack

* Repeat sending logs that were not successfully accepted by Better Stack

* Accept all 2xx status codes as successful

* Ensure reflushing on non-2xx status code or when queue overfilled

Author: PetrHeinz

src/main/java/com/logtail/logback/LogtailAppender.java

@@ -126,19 +126,24 @@ protected void flush() {
         if (isFlushing.getAndSet(true))
             return;
 
-        this.mustReflush = false;
+        mustReflush = false;
 
         try {
             int flushedSize = batch.size();
+            if (flushedSize > batchSize) {
+                flushedSize = batchSize;
+                mustReflush = true;
+            }
 
             LogtailResponse response = callHttpURLConnection(flushedSize);
 
-            if (response.getStatus() != 202) {
+            if (response.getStatus() >= 200 && response.getStatus() < 300) {
+                batch.subList(0, flushedSize).clear();
+                this.warnAboutMaxQueueSize = true;
+            } else {
                 errorLog.error("Error calling Better Stack : {} ({})", response.getError(), response.getStatus());
+                mustReflush = true;
             }
-
-            batch.subList(0, flushedSize).clear();
-            this.warnAboutMaxQueueSize = true;
         } catch (JsonProcessingException e) {
             errorLog.error("Error processing JSON data : {}", e.getMessage(), e);
 
@@ -148,7 +153,7 @@ protected void flush() {
 
         isFlushing.set(false);
 
-        if (this.mustReflush || batch.size() >= batchSize)
+        if (mustReflush || batch.size() >= batchSize)
             flush();
     }