update: update custom monitoring templates

Created by: huanggze

Signed-off-by: huanggze loganhuang@yunify.com

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change

/kind bug

/kind cleanup /kind design /kind documentation /kind failing-test /kind feature /kind flake

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Special notes for reviewers:

• update template content (most important)
• change legend variable format from {} to {{}}
• change valueName from avg to last
• remove the follwing redudant fields.

Additional documentation, usage docs, etc.: