[Features] cases enhancement & alerts triage

**Cases**
Please, can you add the possibility to

- add the alerts to an existing case (ie also after the case was created)
- add observables to an existing case (ie also after the case was created)

Start by locating the TypeScript entry points for case creation and the existing alert and observable handling. Trace how a case is represented after creation and identify the flow used to attach its initial data. Done means an existing case can accept alerts and observables after it has been created, with the relevant behavior covered by the project's tests if available.

Written by the indexing model from the issue text.