docs(logging): improve write log entry sample

[MukundaKatta]

Fixes #11923.

Updates the Java Cloud Logging write log entry sample to demonstrate:

• textPayload and jsonPayload entries
• severity, labels, and the global monitored resource
• writing one log entry and writing a batch of entries

The accompanying sample test now asserts the constructed entry metadata and payload types before exercising the sample.

Verification:

• git diff --check

Not run locally:

• mvn -pl java-logging/samples/snippets -Dtest=LoggingIT#testWriteLogEntrySample test (mvn is not installed in this environment)

[gemini-code-assist]

Code Review

This pull request refactors the WriteLogEntry sample to demonstrate both single and batch log writing by introducing a createLogEntries helper method. It also enhances the integration tests to validate the specific attributes of the generated log entries. Review feedback suggests avoiding duplicate log writes by using a sublist for the batch operation and renaming a variable that shadows the JsonPayload class to improve clarity.

[gemini-code-assist]

The current implementation writes the first entry (entries.get(0)) twice: once individually at line 44 and again as part of the batch at line 47. This will result in duplicate log entries in Cloud Logging. While this demonstrates both APIs, it might be confusing for users. Consider using distinct entries or a sublist for the batch write to avoid duplication.

Suggested change

	logging.write(Collections.singleton(entries.get(0)));
	// Writes a batch of text and structured log entries.
	logging.write(entries);
	// Writes one text log entry.
	logging.write(Collections.singleton(entries.get(0)));
	// Writes a batch of structured log entries.
	logging.write(entries.subList(1, entries.size()));

[gemini-code-assist]

The local variable jsonPayload shadows the JsonPayload class name (differing only by case), which is imported and used in the same scope (line 71). This can lead to confusion and is generally discouraged in Java. Consider renaming the variable to payload or payloadMap.

Suggested change

	Map<String, Object> jsonPayload =
	ImmutableMap.of(
	"message", "Structured log entry written from Java.", "component", "sample");
	LogEntry structEntry =
	LogEntry.newBuilder(JsonPayload.of(jsonPayload))
	Map<String, Object> payload =
	ImmutableMap.of(
	"message", "Structured log entry written from Java.", "component", "sample");
	LogEntry structEntry =
	LogEntry.newBuilder(JsonPayload.of(payload))