Resolve "Add an input block to define the systems to run"

Description

New input block Systems to define a list of systems to run. It is now possible to have more than one system, although there are still not interactions between them. The different systems are stored in a linked list of polymorphic objects, so that it can store different types of systems.

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Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

Closes #191 (closed)