docs: standardize environment variable tables and refactor settings

- Add 'Required' and 'Default' columns to all environment variable documentation tables.
- Refactor all Settings classes to inherit from a new CommonSettings base class in templates/settings.py.
- Consolidate 'service_name', 'metrics_namespace', and 'log_level' into CommonSettings.
- Ensure all templates have template-specific defaults in their Settings subclasses.
- Fix Environment variables table ordering in EventBridge documentation.
- Update EventBridge property tests to reflect optional settings.
- Document UX learnings in .jules/palette.md.

Author: google-labs-jules[bot]

templates/settings.py

@@ -1,12 +1,10 @@
-from pydantic import ConfigDict, Field
+from pydantic import Field
 from pydantic_settings import BaseSettings
 
 
 class CommonSettings(BaseSettings):
     """Common settings shared by all Lambda functions."""
 
-    model_config = ConfigDict(case_sensitive=False)
-
     service_name: str = Field(description="Powertools service name")
     metrics_namespace: str = Field(description="Powertools metrics namespace")
     log_level: str = Field(description="Logging level", default="INFO")