Make CODEOWNERS more specific (#240)

Author: Marenz

CODEOWNERS

@@ -4,4 +4,4 @@
 # Fallback owner.
 # These are the default owners for everything in the repo, unless a later match
 # takes precedence.
-* @frequenz-floss/api-dispatch-team @frequenz-floss/python-sdk-team
+/{src,tests,docs,dist}/ @frequenz-floss/api-dispatch-team @frequenz-floss/python-sdk-team