[2.2.0] Checkmk Werk 16387 created: notification_rules: custom plugins now created correctly when using the REST-API

Title: notification_rules: custom plugins now created correctly when using the REST-API Class: fix Compatible: compat Component: rest-api Date: 1705911511 Edition: cre Level: 1 Version: 2.2.0p22 Previous to this werk, when creating a notification rule with a custom plugin via the rest-api, the parameters were not being shown in the UI as expected. The reason being, an incorrect format being saved to file. This werk addresses this issue by correcting the format being saved to file.