Allow copy-paste of env variables or upload of env file

**Tell us about your request**
Some apps that I have deployed to App Runner do have a lot of env variables (>30). When copy-pasting each variable, it takes a lot of time to set up or update a service.

**Describe alternatives you've considered**
On Vercel it's possible to copy a whole env file and paste it into the wizard when creating an app/service on the platform. The content gets automatically parsed, and the variables are separated into the name and value of the variable. This allows adding a lot of variables within a few seconds.
Another alternative would be the upload of an existing env file.