Replace stringLeading method with Java 8 friendlty alternative (aws-observability#902)

*Issue #, if available:*
The stringLeading method is only available in Java 11+. This doesn't
meet our requirement of ADOT Java being available for Java 8+. We need
to find an alternative method.

*Description of changes:*
Refactor code to be Java 8 friendlty

*Test run:*

https://github.com/aws-observability/aws-otel-java-instrumentation/actions/runs/11158858146

*Note*
Previously, the test was failing Java 8 for EKS use case. With this new
change, it is passing now.
This proves that:
1. The function `getDBStatementRemoteOperation`, specfically
`stripLeading()` is being tested by E2E test
2. The new change does not affect Java 11+ and also fixes Java 8

Unit tests also show that combinations of different attributes all pass
([Link](https://github.com/aws-observability/aws-otel-java-instrumentation/blob/main/awsagentprovider/src/test/java/software/amazon/opentelemetry/javaagent/providers/AwsMetricAttributeGeneratorTest.java#L573))


By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Author: harrryr

awsagentprovider/src/main/java/software/amazon/opentelemetry/javaagent/providers/AwsMetricAttributeGenerator.java

@@ -640,7 +640,7 @@ private static String getDBStatementRemoteOperation(
 
     // Remove all whitespace and newline characters from the beginning of remote_operation
     // and retrieve the first MAX_KEYWORD_LENGTH characters
-    remoteOperation = remoteOperation.stripLeading();
+    remoteOperation = remoteOperation.replaceFirst("^\\s+", "");
     if (remoteOperation.length() > MAX_KEYWORD_LENGTH) {
       remoteOperation = remoteOperation.substring(0, MAX_KEYWORD_LENGTH);
     }