Adjust GenericVersionStorageProvider to no longer save additionalHeaders in shared_plugin_data

[six7]

https://hyma-team.slack.com/archives/C04V8U8UH0F/p1761936841067519

adjust generic versioned storage provider to not store additionalHeaders in sharedplugindata, but in client storage only. right now it seems to be stored in both. but additionalHeaders can contain sensitive data, so it needs to be in client storage.

given users already have data there - make sure that we do this on launch of the plugin (like a migration step - invisible to the user, part of our startup processes). and then whenever they create or edit one, we dont save to shared plugin data).

also noticed a bug with generic versioned where if you edit the storage provider we seem to cause all values to be reset to just options but tokens no longer exist. seems to override whatever the user has with an empty object.

[stephanieea]

We are also observing syncing behavior with respect to the Token Studio license keys. One user added a license key and then a separate user received a notification that there account had been suspended. On closer inspection they saw their license key had changed and their header information had changed to match what the other user had entered.