Handle Participant Unavailable Notification.story

When the ｟CSM｠ sends a Participant Unavailable

Then ｟the IPF｠ receives a Participant Unavailable Notification using predicate:
| requestId | participant-unavailable |
| version.major | 1 |
| version.minor | 0 |
| version.patch | 0 |
| payload.content.csm | RT1 |
| payload.content.participantId | IPSTFRPP |
| payload.content.rawMessage | prettyPrint(#ParticipantUnavailable) |
| payload.version.major | 1 |
| payload.version.minor | 0 |
| payload.version.patch | 0 |