[FEATURE] split notification config into seperate template

[h3o66]

User Story

As a developer I want to have the development easier and less duplication in the server configs

Basic info

Move the notification part into a seperate template like _default_notification.cfg This holds only the basic notification template to split it to a seperate file.

Further Information

TBD:

• [ ] create seperate template for the notification
• [ ] add new config to init and update
• [ ] remove config snippets from all server _default.cfg files

[h3o66]

update: made this PR more general to prevent duplicates

[h3o66]

Related to #1732 imho