Goal:

Merge foreman-tasks plugin into foreman.

Acceptance Criteria:

• foreman-tasks code is included in foreman itself
• rubygem-foreman-tasks becomes only a shim depending on a high-enough version of foreman to ease the transition
• no new functionality is added, no old functionality is removed, tests should keeping passing without any changes
• all configuration files and installer options remain unchanged
• drop dependency on tasks from other plugins
• the theforeman/foreman-tasks repository on github is archived

Open questions:

• Should hammer-cli-foreman-tasks be merged into hammer-cli-foreman as well?
• Should it be fully integrated (ie removing the ForemanTasks namespace) or be kept as a separate engine, living in the same codebase?
• Should we rename "Tasks plugin" component to just "Tasks"/"Tasking"/"Background processing" as it won't be a plugin anymore?