Changes to cases in 8.8

[nastasha-solomon]

Description

The cases details page is getting a small overhaul in 8.8.

Notable changes include:

• The description is kept separate from the comment/activity history.
• Three new tabs have been added above the comment/activity history section:
  • All: Displays comments and a history of user activity on the case.
  • Comments: Displays all comments added to the case.
  • History: Displays the fully user activity history in the case.
• Users can sort comments and case activity to show the oldest or newest first (verify this)
  In addition, users will now be able to attach (and remove) files to cases.
• Users can remove alerts from the UI.
  
  • After an alert is removed, it's logged in the case history.
  
• Users can copy a reference link to specific case activity (verify that this is new in 8.8)

Related:

• [Cases][Meta]: File attachments kibana#151595
• [Cases] Detail View Attachments Table kibana#152941

Required doc updates

TBD

Notes

• The case summary (case KPIs) will still be present in Security cases. It's not there in Observability cases.
• Work with @christos or @jonathan-buttner to write summaries for release notes and what's new.

[nastasha-solomon]

Changes covered in #3171.