Make custom thread pool size configurable.

Fix processing build request in one thread.

server/src/main/java/com/defold/extender/AsyncBuilder.java

@@ -83,7 +83,7 @@ private void writeExceptionToFile(Exception exception, File file) {
         }
     }
 
-    @Async
+    @Async(value="extenderTaskExecutor")
     public void asyncBuildEngine(MetricsWriter metricsWriter, String platform, String sdkVersion,
             File jobDirectory, File uploadDirectory, File buildDirectory) throws IOException {
         String jobName = jobDirectory.getName();

server/src/main/java/com/defold/extender/tracing/ExtenderExecutor.java

@@ -1,5 +1,6 @@
 package com.defold.extender.tracing;
 
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.task.SimpleAsyncTaskExecutor;
@@ -24,6 +25,9 @@
 @Configuration(proxyBeanMethods = false)
 class ExtenderExecutor {
 
+    @Value("${extender.tasks.executor.pool-size:35}")
+    private int executorPoolSize;
+
     @Configuration(proxyBeanMethods = false)
     @EnableAsync
     static class AsyncConfig implements AsyncConfigurer, WebMvcConfigurer {
@@ -63,6 +67,7 @@ public ScheduledExecutorService getScheduledExecutor() throws IllegalStateExcept
                     return ContextScheduledExecutorService.wrap(super.getScheduledExecutor());
                 }
         };
+        threadPoolTaskScheduler.setPoolSize(executorPoolSize);
         threadPoolTaskScheduler.initialize();
         return threadPoolTaskScheduler;
     }