Add support for providing environment var/values in a `.env` file read by `dotenv.net`

[Aniruddh25]

Discussed in #1361

^{Originally posted by glaucia86 March 25, 2023}

Hi!

I would like to propose that we can make use of the .env file in the dab.config.json file.
As it already happens with the files generated by the SWA CLI: staticwebapp.database.config.json (example: HERE)

Because the connection string is very exposed, where it has extremely sensitive data such as: login, password and database name.

This issue is to add support for .env so that I can just put my sensitive data into the .env, if I don't need the complexity of having multiple configuration files.

This is separate from the current @env() feature where we need to set environment variables on the system.

[yorek]

Two libraries for this option:

• https://github.com/tonerdo/dotnet-env
• https://github.com/bolorundurowb/dotenv.net