Agent names using `%n` now receive a random suffix

Agent names containing %n now receive a random six-character alphanumeric suffix instead of the next available number. For example, cool-agent-%n , which previously produced a name such as cool-agent-123 , now produces a name such as cool-agent-aB3dE6 . We deprecated %n in 2022 because allocating sequential agent names becomes increasingly expensive as organizations scale.