Added advanced type annotations (title, description, extra, etc...)

[rgusmero]

Added a very simple yet powerful annotation api. Instead of specifying a string for the description, you can use a special dataclass with more oprions. e.g.

@DataClass
class C:
x: Annotated[int, DG(title='x', description='This is x')]

NOTE: An advanced example is present in the tests - it also shows the use of generic jsonschema annotations (via schema_extra field) both at the dataclass declaration level and at the transform dict level.

Coupling dataglasses with advanced jsonschema tools like jsonmerge, allors e.g. merging config files with specific merge strategies.