The limit is stored in and read from MSS key state and now we preserve
state data even when the key becomes underprivileged.
We don't need to refresh anything and also the checking underprivileged key
would return 403 and no data about limits.
[MAILPOET-5191]
When the shop blocked access for an API key due subscriber limit it used
to set the error as "Insufficient privileges," and that was in the plugin
interpreted same as "Subscribers limit reached".
The SHOP-1228 changes the error message will be set to "Subscribers limit reached".
This commit updates the error mapper to be able to process the new error message.
It also keeps the old approach for previously blocked keys.
[MAILPOET-5191]
