command/init: Merge duplicated PSS logic back into existing codepath (#38227)

Author: radeksimko

.changes/v1.15/NOTES-20260303-115443.yaml

@@ -0,0 +1,5 @@
+kind: NOTES
+body: 'command/init: Provider installation was refactored to enable future enhancements in the area. This results in different order of operations during init and 2 new log messages replacing one (`initializing_provider_plugin_message`). The change should not have any end-user impact aside from the `init` command output.'
+time: 2026-03-03T11:54:43.732353Z
+custom:
+    Issue: "38227"

internal/backend/init/init.go

@@ -93,6 +93,13 @@ func Backend(name string) backend.InitFn {
 	return backends[name]
 }
 
+func BackendExists(name string) bool {
+	backendsLock.Lock()
+	defer backendsLock.Unlock()
+	_, ok := backends[name]
+	return ok
+}
+
 // Set sets a new backend in the list of backends. If f is nil then the
 // backend will be removed from the map. If this backend already exists
 // then it will be overwritten.