Adding Server Groups And Removing Validating Schema Structure To Better Align With REST API Using Pedantic

[XaverStiensmeier]

Added the key serverGroup both on instance and configuration level. Setting a previously created serverGroup allows users to influence whether their VMs are scheduled on the same or different hypervisors. This is helpful to spread the load of large machines. Works now both for permanent instances and on demand scheduled workers. See #688

In the past BiBiGrid used schema for validation in regular use and pedantic for REST with fastapi. This PR removed the schema validation and replaced it with pedantic. This avoids having two different sources of validation truth which caused minor deviations in the past.
However, switching to pedantic also revealed a conceptual issue of the bibigrid yaml format that makes it difficult to validate; having one list for all configs where the first element of that list has other values than the rest. While a hack has been implemented to allow for intuitive validation via pedantic that produces helpful error messages, simplifying the config should be considered. As this is a change of the configuration that also affects users, this should likely happen in a major version change (related issue #690).

A few inconsistencies between the schema and pedantic have been fixed:

• REST is now also strict and will throw an error if a key is passed that is not defined in the pedantic models
• A few previously undefined keys are now defined including meta and securityGroup

closes #688

[XaverStiensmeier]

@dweinholz this pull requests makes the validation of the configuration more strict. This also affects REST which therefore affects SimpleVM. This only requires change if SimpleVM defined additional keys or set unexpected types for certain keys.

[jkrue]

lgtm