[SPARK-52559] Synchronize SparkOperatorConfManager.getValue

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to fix a concurrency issue by synchronizing SparkOperatorConfManager.getValue.

Why are the changes needed?

configOverrides is supposed by being protected by this at refresh method.

spark-kubernetes-operator/spark-operator/src/main/java/org/apache/spark/k8s/operator/config/SparkOperatorConfManager.java

Lines 71 to 76 in 35214b0

	public void refresh(Map<String, String> updatedConfig) {
	synchronized (this) {
	this.configOverrides = new Properties();
	configOverrides.putAll(updatedConfig);
	}
	}

However, currently getValue can access an empty value while refresh invokes this.configOverrides = new Properties(); statement because getValue method is not synchronized properly.

spark-kubernetes-operator/spark-operator/src/main/java/org/apache/spark/k8s/operator/config/SparkOperatorConfManager.java

Lines 62 to 65 in 35214b0

	public String getValue(String key) {
	String currentValue = configOverrides.getProperty(key);
	return StringUtils.isEmpty(currentValue) ? getInitialValue(key) : currentValue;
	}

Does this PR introduce any user-facing change?

Yes, this is a bug fix.

How was this patch tested?

Manual review. (It's a little difficult to add a concurrency failure test case).

Was this patch authored or co-authored using generative AI tooling?

No.

[dongjoon-hyun]

cc @viirya , @jiangzho

[dongjoon-hyun]

Thank you, @viirya ! Merged to main.