[Cases] Files gallery view

[adcoelho]

Subtask of #151595

Summary

Users should have a way to attach and visualize attached files to a case.

In the Cases detail view, there is a tab with the name Files.

Under this tab there should be two visualization options for the files attached to a case:

1. [Cases] Attachments table view #151723
2. A list of file previews(including thumbnails) to be developed in this issue.

Requirements

• The attachments preview list should display:

  • A preview of the case attachment which can be:
    • An image thumbnail
    • A placeholder thumbnail for files of non-image types
  • File name
  • File size
  • Download action
  • Delete action

• The attachments preview list has the following features:

  • a configurable number of rows
  • pagination

• The preview list should be:

  • searchable by file name
    

  • filterable by file type
    

• The user should be able to upload/attach files to a case
  

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[elasticmachine]

Pinging @elastic/response-ops-cases (Feature:Cases)