YARN-11360: Proposed "yarn top" output change

[Chris Nauroth <cn...@apache.org>]

I'd like to raise awareness that in YARN-11360, I've shared a patch that
includes proposed changes to the header output of the "yarn top" CLI.
Technically, this doesn't follow the letter of the law on CLI output
compatibility [1]. However, I'd like to proceed on the basis that "yarn
top" is intended as an interactive tool for users actively watching, and it
seems unlikely that anyone could usefully script around its output anyway.

The patch already has a +1. I'll hold off committing for a few days. Please
reply if you have an opinion. If there isn't consensus, I can revert the
"yarn top" portion of the patch, leaving just the protocol changes. Then,
the "yarn top" changes would go in a separate patch targeting a major
release upgrade that allows backward-incompatible changes. (I don't believe
there is a branch to receive 4.x changes though, so this would effectively
stall that part of the patch indefinitely.)

[1]
https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/Compatibility.html#Command_Line_Interface_.28CLI.29

Chris Nauroth