Support for v1/v2 config blocks

- Backwards compatiblity shims from v2 to v1 configs
- config merging for v2
- compatibility shim for parsing/contexts
- defer var lookups as late as possible
- fixed ContextConfigType to be a proper Union of the two context config types
- Fix adapter configs to be proper dataclasses
- fix unused config paths error
- make v2 config parsing not alter its source data


automatic commit by git-black, original commits:
  c7d8031
  fac8a28

core/dbt/parser/base.py

@@ -314,9 +314,7 @@ def update_parsed_node_config(
             get_rendered(hook.sql, context, parsed_node, capture_macros=True)
 
     def initial_config(self, fqn: List[str]) -> ContextConfig:
-        config_version = min(
-            [self.project.config_version, self.root_project.config_version]
-        )
+        config_version = min([self.project.config_version, self.root_project.config_version])
         if config_version == 2:
             return ContextConfig(
                 self.root_project,