eZ Platform Enterprise is a "commercial extended" version of ez Platform that includes, among other things, support for push-based purging on the Fastly CDN.
eZ Platform's documentation includes instructions on how to configure eZ Platform for Fastly. Follow the steps there to prepare eZ Platform for Fastly.
The best way to provide the Fastly credentials and configuration to eZ Platform on Platform.sh is via environment variables. That way private credentials are never stored in Git.
Using the CLI, run the following commands to set the configuration on your master environment. (Note that they will inherit to all other environments by default unless overridden.)
platform variable:create -e master --level environment env:HTTPCACHE_PURGE_TYPE --value 'fastly' platform variable:create -e master --level environment env:FASTLY_SERVICE_ID --value 'YOUR_ID_HERE' platform variable:create -e master --level environment env:FASTLY_KEY --value 'YOUR_ID_HERE'
YOUR_ID_HERE with the Fastly Service ID and Key obtained from Fastly.
See the alternate Go-live process for Fastly on Platform.sh. This process is the same for any application.