Skip adding dimensions with empty dimension value into default dimension

[paggynie]

Issue #, if available:
#125

Description of changes:
Customer with ECS FireLens now has problem to flush metrics logger when using default dimension because we return "" for log group name but we throw InvalidDimensionException when setting the empty dimension. Example stack trace

software.amazon.cloudwatchlogs.emf.exception.InvalidDimensionException: Dimension value cannot be empty
at software.amazon.cloudwatchlogs.emf.util.Validator.validateDimensionSet(Validator.java:48)
at software.amazon.cloudwatchlogs.emf.model.DimensionSet.addDimension(DimensionSet.java:167)
at software.amazon.cloudwatchlogs.emf.logger.MetricsLogger.configureContextForEnvironment(MetricsLogger.java:268)
at software.amazon.cloudwatchlogs.emf.logger.MetricsLogger.flush(MetricsLogger.java:91)
at com.amazonaws.toledo.telemetry.common.util.MetricsPublisher.flush(MetricsPublisher.java:39)
at com.amazonaws.toledo.telemetry.streamprocessor.StreamProcessor.processRecords(StreamProcessor.java:147)
at com.amazonaws.services.kinesis.clientlibrary.lib.worker.ProcessTask.callProcessRecords(ProcessTask.java:221)
at com.amazonaws.services.kinesis.clientlibrary.lib.worker.ProcessTask.call(ProcessTask.java:176)
at com.amazonaws.services.kinesis.clientlibrary.lib.worker.MetricsCollectingTaskDecorator.call(MetricsCollectingTaskDecorator.java:49)
at com.amazonaws.services.kinesis.clientlibrary.lib.worker.MetricsCollectingTaskDecorator.call(MetricsCollectingTaskDecorator.java:24)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:829)

This change is to skip adding dimension if dimension value is null or empty

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[markkuhn]

@paggynie Build is failing due to spotless. Please run ./gradlew :spotlessApply to fix it.

[markkuhn]

🚀