Move Global Variables into User Settings Global

[phreed]

User global environment variables are new, since v3.1

• https://nodered.org/docs/user-guide/environment-variables#global-environment-variables
• https://nodered.org/blog/2023/09/06/version-3-1-released#global-environment-variables

These are global variables at the top level of node-red.
Previously, the variables were only global at the flow (subflows, groups) level.

See https://discourse.nodered.org/t/construting-flow-subflow-and-group-global-variables-from-user-global-variables/92316/2
for relevant comments.