Paginate list_requests DynamoDb.scan

[manics]

Description

DynamoDB has a 1MB limit on responses. Pagination is needed for scanning larger tables.
https://stackoverflow.com/questions/36780856/complete-scan-of-dynamodb-with-boto3/38619425#38619425

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Declaration : By submitting this pull request, I confirm that my
contribution is made under the terms of the Apache-2.0 license

[manics]

Tested with this temporary local change to check the pagination logic:

diff --git a/egress_backend/lambda/egress_api/list_requests.py b/egress_backend/lambda/egress_api/list_requests.py
index c4b3250..d3f8d43 100644
--- a/egress_backend/lambda/egress_api/list_requests.py
+++ b/egress_backend/lambda/egress_api/list_requests.py
@@ -20,10 +20,12 @@ def list_requests():
 
     ddb_table = ddb.Table(table)
 
-    response = ddb_table.scan()
+    response = ddb_table.scan(Limit=10)
+    print(response)
     data = response["Items"]
     while response.get("LastEvaluatedKey"):
         response = ddb_table.scan(ExclusiveStartKey=response["LastEvaluatedKey"])
+        print(response)
         data.extend(response["Items"])
 
     logger.debug("Successful database scan of all egress requests")