Add environment variables

[Danilo Cadena]

Is your feature request related to a problem? Please describe.
My project uses "Netlify Functions" and these functions need environment variables to work properly. My problem is that the environment variable used by the functions is not available when running the project in development mode. this is my setup.

Describe the solution you'd like
Being able to add the environment variables that my project needs so that when the commands of the "start" property are executed, they are already available.
e.g. on github actions:

Describe alternatives you've considered
Create the variables with the prefix "CYPRESS_"