style: update logback configuration and log levels

- Comment out configuration block in logback.xml
- Modify log level 'WARNING' to 'WARN' in FlutterLogbackAppender.java

Author: muzahidul-opti

android/src/main/assets/logback.xml

@@ -1,4 +1,4 @@
-<configuration
+<!-- <configuration
     xmlns="https://tony19.github.io/logback-android/xml"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="https://tony19.github.io/logback-android/xml https://cdn.jsdelivr.net/gh/tony19/logback-android/logback.xsd"
@@ -15,4 +15,4 @@
     <root level="DEBUG">
         <appender-ref ref="logcat" />
     </root>
-</configuration>
+</configuration> -->

android/src/main/java/com/optimizely/optimizely_flutter_sdk/FlutterLogbackAppender.java

@@ -50,7 +50,6 @@ int convertLogLevel(String logLevel) {
             case "ERROR":
                 return 1;
             case "WARN":
-            case "WARNING":
                 return 2;
             case "INFO":
                 return 3;