Refactor .utc.iso8601(3) to single method

What does this MR do?

Refactor .utc.iso8601(3) to single method. This is to improve the consistency of timestamp log format in loggings.

For example: Time.now.utc.iso8601(3) will be Time.now.log_format after refactoring.

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #207215 (closed)