fix(hub): System.HasUser - return true if SHARE_ALL_SYSTEMS=true (#1891)

- move hub's GetEnv function to new utils package to more easily share
across different hub packages
- change System.HasUser to take core.Record instead of user ID string
- add tests

internal/hub/utils/utils.go

@@ -0,0 +1,12 @@
+// Package utils provides utility functions for the hub.
+package utils
+
+import "os"
+
+// GetEnv retrieves an environment variable with a "BESZEL_HUB_" prefix, or falls back to the unprefixed key.
+func GetEnv(key string) (value string, exists bool) {
+	if value, exists = os.LookupEnv("BESZEL_HUB_" + key); exists {
+		return value, exists
+	}
+	return os.LookupEnv(key)
+}