Create compatibilty setting on SavedScenario

[noracato]

In the engine, all scenarios have a keep compatible attribute set to true or false to indicate whether they should join migrations or not. When a user saves a scenario as a SavedScenario, the last version is automatically set to keep_compatible: true. It would be nice to let users opt in or out of this behaviour. Therefor we can add a new option to a SavedScenario.

• Create new attribute on SavedScenario keep_compatible
• Adjust the behaviour on the create and update services of SavedScenarios
• Show the value of this new attribute somewhere in the (saved) scenario view (not too visible not to confuse users too much about this expert feature)
• Create a place to change this setting with some well documented consequences of opting out.
• OPTIONAL/TO DISCUSS: create a third option for compatibility where ALL scenarios in the history are being kept compatible

[github-actions]

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