Eagerly requiring Rake could put 100ms on to the Rails boot time. Shimmy that
down to 0 by requiring Rake when no native Rails command exists and we try to
run a Rake task. Or when printing all the Rake commands through `rails help`.
Fixes#25029
Allows any Rake task to be run through `bin/rails` such as `bin/rails db:migrate`,
`bin/rails notes` etc.
The Rake tasks are appended to Rails' help output, and blend in as standard commands.
