docs(event_handler): add information about case-insensitive header lookup function (#3183)

Co-authored-by: Leandro Damascena <lcdama@amazon.pt>
Co-authored-by: Heitor Lessa <lessa@amazon.nl>

Author: 3 people

aws_lambda_powertools/utilities/data_classes/common.py

@@ -189,7 +189,7 @@ def get_header_value(
         default_value: str, optional
             Default value if no value was found by name
         case_sensitive: bool
-            Whether to use a case-sensitive look up
+            Whether to use a case-sensitive look up. By default we make a case-insensitive lookup.
         Returns
         -------
         str, optional

docs/core/event_handler/api_gateway.md

@@ -239,7 +239,7 @@ You can access the raw payload via `body` property, or if it's a JSON string you
 
 #### Headers
 
-Similarly to [Query strings](#query-strings-and-payload), you can access headers as dictionary via `app.current_event.headers`, or by name via `get_header_value`.
+Similarly to [Query strings](#query-strings-and-payload), you can access headers as dictionary via `app.current_event.headers`, or by name via `get_header_value`. If you prefer a case-insensitive lookup of the header value, the `app.current_event.get_header_value` function automatically handles it.
 
 ```python hl_lines="19" title="Accessing HTTP Headers"
 --8<-- "examples/event_handler_rest/src/accessing_request_details_headers.py"