Fixes #30670 - start dynflow client in report tasks

As reported, a single foreman-rake reports:daily in fact triggers the
rake task twice. This is caused by plugins that need to extend this (and
similar tasks) with their own logic and add other rake tasks
dependencies. For that they need to `load` our core tasks, causing the
duplication. `load` should be avoided entirely.

In this specific case though, the need was to add dynflow:client
dependecy to reports, since Katello plugin may schedule some dynflow
job as part of that. Therefore it needs client connection to dynflow.
This task does not start the executor.

Instead of asking all plugins to add such dependency if their custom
mail notification requires dynflow client, the Foreman core should offer
this by default.

The real fix needs to land in Katello, it should no longer load the core
task definition, however in order for that to be possible, this PR needs
to be merged first.

• modify the Katello in a way requiring the task does not cause
  duplicity
• clearing the task after it's loaded - this helps but may have other
  consequences and does not solve the issue for other plugins

Refs #30670 - dynflow client depends on environment