[BUG] Amazon Security Lake validation step uses invalid file name

[AlexRuiz7]

Description

During the internal testing of #128, it was reported that the file name used to perform the validation of the integration is incorrect, as it does not match the file name pattern used by Logstash, which is expected by the Lambda's function code.

The code extracts information, such as the date, from the file's name, so using just sample.txt as stated in the documentation does not work.