FAST ng: stage 0 environments and VPC-SC IaC resources

[ludoo]

This is the first PR adding supporting resources for a different resource management stage.

This only changes stage 0 with no actual impact on existing installations, by

• adding an environments variable and using the default environment name defined there instead of the static prod name
• adding the environments variable to globals outputs for consumption by the following stages (implemented in later PRs)
• adding service account, bucket and CI/CD resources for the dedicated VPC SC stage (implemented in a later PR)