FIX: Mark size and eTag as optional attributes

Fixes ObjectRemoved API event, as they don't include these attributes.
#1637

Signed-off-by: Diego Barreiro <[email protected]>

Author: barreeeiroo

Diff for: aws_lambda_powertools/utilities/parser/models/s3.py

@@ -43,8 +43,8 @@ class S3Bucket(BaseModel):
 
 class S3Object(BaseModel):
     key: str
-    size: NonNegativeFloat
-    eTag: str
+    size: Optional[NonNegativeFloat]
+    eTag: Optional[str]
     sequencer: str
     versionId: Optional[str]