[ZEPPELIN-6496] Replace BigQuery polling stdout output with SLF4J logging

[celinayk]

What is this PR for?

BigQueryInterpreter.pollJob(...) printed job polling status directly to standard output via System.out.println(...), bypassing Zeppelin's SLF4J/Log4j2 logging
configuration, log levels, and appenders. This made diagnostics noisy and hard to route in server/interpreter deployments. This PR replaces the direct stdout call with a
structured SLF4J logger call.

What type of PR is it?

Improvement

Todos

• Replace System.out.println(...) in pollJob(...) with LOGGER.info(...)
• Preserve job state and wait interval information in the log message
• No behavior changes to polling, sleeping, or returned job handling

What is the Jira issue?

ZEPPELIN-6496

How should this be tested?

• rg -n "System\.out\.println|System\.err\.println" bigquery/src/main/java/org/apache/zeppelin/bigquery returns no results
• ./mvnw test -pl bigquery compiles/builds successfully
• Manually trigger a BigQuery job poll and confirm the state/interval now appears via the configured logger instead of raw stdout

Screenshots (if appropriate)

N/A

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[ParkGyeongTae]

LGTM. The change correctly replaces the System.out.println in pollJob()
with LOGGER.info(...), which is already declared in the class.

Using SLF4J parameterized logging ({}) is a small additional improvement
over the original string concatenation — it avoids unnecessary string
construction when the INFO level is disabled.

Verified:

• No remaining System.out/System.err calls in the bigquery package.
• Polling behavior (while loop, Thread.sleep, returned Job) is unchanged.

Nit: The PR title appears to be truncated — could you update it to
[ZEPPELIN-6496] Replace BigQuery polling stdout output with SLF4J logging?

[jongyoul]

Reviewed the current head. The logging-only change preserves BigQuery polling behavior, and the remaining Selenium failure is unrelated to this module.

[celinayk]

Thanks for the reviews! Updated the PR title to the full form as suggested.

[jongyoul]

Merged into master (8b0bf9c).