[improve][fn] Standardize log4j2 Root logger configuration to use system property

[sandeep-mst]

Fixes #23783

Motivation

Both java_instance_log4j2.xml and kubernetes_instance_log4j2.xml had their Root logger levels hardcoded to 'info', which prevented the pulsar.log.level system property from controlling the actual logging level. While the system property was defined in both files, it was only being applied at the AppenderRef level.

Modifications

Updated both log4j2 configuration files in pulsar-functions/runtime-all/src/main/resources/:

• Changed Root logger <level> from hardcoded info to ${sys:pulsar.log.level:-info}
• Removed the <level> attribute from the AppenderRef element

Both files now consistently use the ${sys:pulsar.log.level} system property at the Root logger level, enabling proper dynamic log level control.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

[sandeep-mst]

/pulsarbot rerun-failure-checks

[sandeep-mst]

@merlimat Please merge the PR if nothing else is required on it.