doc(architecture): update the ordering of vertical and horizontal headers in the statement

[vaishnavyogesh]

The line here seems to be incorrect since according to the table vertical headers denote LoggerConfig Level while horizontal ones denote LogEvent Level.

This MR updates the ordering to correctly explain the table beneath it.

Checklist

• Base your changes on 2.x branch if you are targeting Log4j 2; use main otherwise
• ./mvnw verify succeeds (if it fails due to code formatting issues reported by Spotless, simply run ./mvnw spotless:apply and retry)
• Non-trivial changes contain an entry file in the src/changelog/.2.x.x directory
• Tests for the changes are provided
• Commits are signed (optional, but highly recommended)

[vy]

@vaishnavyogesh, thanks so much for taking time review these and submit a correction. Unfortunately, main is substantially behind 2.x in terms of, among other things, documentation. It would be really helpful if you can port architecture.adoc from 2.x to main instead. Please make sure to verify your changes with ./mvnw site as as explained here.