Update behaviour for `immutable` and `computed` properties

[yvo-niedrich]

OpenAPI Documentation

• Display computed properties in the Create-OpenApi, if it is also annotated as ComputedDefaultValue
• Hide immutable properties in the Update-OpenApi
• Include GeneratedProperties (in addition to Declared) when generating the Entity OpenAPI documentation

Property Filtering

• Strips computed fields from create operations, unless the property is also annotated as ComputedDefaultValue
• Strips computed fields from update operations

Annotations

• Enum can be annotated as nullable and immutable

Changes

• Default drivers key properties (with a default value) are annotated as Computed - instead of ComputedDefault
• Guid properties are properly validated (thanks @sean-james-eco)

Bugfixes

• Initialise the $cookie property of a request when converting Illuminate\Request. Fixes "Request::$cookies must not be accessed before initialization" when Telescope and APP_DEBUG are enabled.
• EloquentEntitySet::create complies with attribute.source for navigation source (thanks @sean-james-eco)