State why usage ping can't be enabled through the admin area when disabled via config

In the admin area, Usage Ping can't be enabled when it's disabled via gitlab.rb (see docs)

It would be nice to be explicit why this checkbox can't be enabled by stating it, e.g.

Usage Ping can't be enabled because it's disabled via gitlab.rb, please change usage_ping_enabled to be true, see our docs for more information https://docs.gitlab.com/ee/development/usage_ping/#disable-usage-ping