Feature request - Switchable config files for multiple environments

**Is your feature request related to a problem? Please describe.**

I often have configurations that I want to work only in pre-production environments. For example, I want to add site-wide authentication only for dev.

**Describe the solution you'd like**

Like the Node.js env files, I would like to create files with the environment name appended(e.g. `staticwebapp.config.develop.json`), and have a mechanism for switching the file for each environment.

**Describe alternatives you've considered**

As a workaround, I have customized the build script to switch the `staticwebapp.config.json` file.
See the following file for an example that works well.
- https://github.com/k-miyake/swa-nuxt-ts/blob/main/.github/workflows/azure-static-web-apps-yellow-forest-05a08f81e.yml

**Additional context**

Once this is accomplished, we can protect dev environment with GitHub auth, for example.