Support reading environment variables passed to skaffold from file (e.g. .env) #4106
Description
Considering skaffold could use environment variables to populate templated fields - https://skaffold.dev/docs/environment/templating/, it would super convenient to have the ability to pass environment variables to skaffold from file - similar to (or the same as) how docker-compose does that.
Originally, this feature request just got lost here - #543.