Hide test-changes from customers (#2585)

This change
* add changes.is_system flag, that will be true when a change should not
be shown in the app
* update all relevant SQL statements
* set is_system when storing a change as part of blast radius llm
testing
* remove obsolete change metering in stripe
* update area51 to show the new flag
* add link to original change (without database consistency to avoid any
interference with regular operations)

GitOrigin-RevId: 462a1444b76bfeeedc7b150edfa4b8f4da0df42f

Author: DavidS-ovm

sdp-go/changes.go

@@ -16,6 +16,14 @@ func (a *ChangeMetadata) GetUUIDParsed() *uuid.UUID {
 	return &u
 }
 
+func (a *ChangeMetadata) GetNullUUID() uuid.NullUUID {
+	u := a.GetUUIDParsed()
+	if u == nil {
+		return uuid.NullUUID{Valid: false}
+	}
+	return uuid.NullUUID{UUID: *u, Valid: true}
+}
+
 func (a *ChangeProperties) GetChangingItemsBookmarkUUIDParsed() *uuid.UUID {
 	u, err := uuid.FromBytes(a.GetChangingItemsBookmarkUUID())
 	if err != nil {