Update Attachment widget UI to be more consistent

[FikriMilano]

Is your feature request related to a problem? Please describe.
@jingtang10 has some concern that the current Attachment widget design won't be consistent for single and multi attachment.

Describe the solution you'd like
@shelaghm provided a new design in which it will be consistent for single and multi attachment.

Describe alternatives you've considered
N/A

Additional context

Would you like to work on the issue?
Yes

[FikriMilano]

cc @f-odhiambo @fredhersch

[FikriMilano]

This ticket will only handle the UI changes for single attachment.
Here's a different ticket for multi attachment #1797