allow to pick schedule for team's on-call

[lexhuismans-wk]

Problem

We have multiple schedules with an escalation policy for our team. For example our team has

• Schedule A
• Schedule B

With escalation policy

• Escalate to A first during the weekend
• Escalate to B first during the week

In the who is on call panel all the participants from all the schedules are shown resulting in the entire team showing up.

Solution

This PR adds an option to add filter for the schedule that you want by adding the schedule ID.