Increased memory usage on the Amazon Corretto runtime

As originally mentioned in https://github.com/Graylog2/graylog-s3-lambda/issues/20#issuecomment-875936881 by @justinjett, when running the `graylog-s3-lambda` function with the newer `java8.al2/amazon-corretto-8` runtime, the function appears to use more memory than before with the `java8` runtime. In order for an existing function to work with the Corretto runtime, it was necessary to increase the memory allocated to the function.