Implementing Null Value Checks on the Intervention tab

[alireza-dhp]

Dear @benitsch, @ja-fra, @andresgruber

To ensure data collection for observations, we suggest implementing a null value check in the intervention tab when the schedule data check option is selected.
For example, if there is no data for a specific observation over a certain period (e.g., 10 minutes), a notification can be sent to participants. This notification can remind them to fill out the LimeSurvey, complete a simple questionnaire, or ensure that their Polar device is connected to the app.