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

[//]: # (werk v2) # notification_rules: custom plugins now created correctly when using the REST-API key | value ---------- | --- date | 2024-01-22T08:18:31+00:00 version | 2.4.0b1 class | fix edition | cre component | rest-api level | 1 compatible | yes 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.