Revert autostart_denylisted_constants default change and document options

[kaylareopelle]

In #2623, we updated the default for autostart.denylisted_constants to include Rails::Command::RakeCommand and Rails::Command::RunnerCommand. This was in response to #2596.

However, #2677, revealed to use that these constants are important for some users of ActiveJob to automatically report background jobs.

Let's revert the new default and provide documentation for the options and benefits of excluding Rails::Command::RakeCommand and Rails::Command::RunnerCommand.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-277238