Revert "Disable Express eTag response header for consistent FF behaviour across FF runtimes  (#433)" (#438)
Revert "Disable Express eTag response header for consistent FF behaviour across FF runtimes  (#433)" (#438)

This reverts commit 195ae300fa3dd0b6b3cde947a6333d28a0da7a6a.
GoogleCloudPlatform/functions-framework-nodejs,GoogleCloudPlatform/functions-framework-nodejs,GoogleCloudPlatform/functions-framework-nodejs