Add attachments to Timeline

[FelixMalfait]

What

We shipped a new timeline that separate the concept of audit logs (immutable event store of everything that happened), from timeline activities (nice user-facing events that can be grouped together and altered).

We now need to display calendar events, messages and attachment in the timeline.

How

• Remove IsNotAuditLogged decorator (but maybe don't commit / tbd deployment strategy)
• In TimelineActivityRepository and add one private function for each type of event
• Edit UpsertTimelineActivityFromInternalEvent to make sure the job is dispatched for those events
• Work on frontend to make sure icon/text displayed makes sense, maybe improve it

[FelixMalfait]

Re-assigning to @Weiko who is working on it this week already