External Form Upload: Display import summary / errors

[khiga8]

🔗 Issue

#1112

✍️ Description

This PR displays import summary feedback when a file is uploaded through the external form upload.

• I opted to display a visually prominent banner right below the attach control, rather than top of the page. This banner is injected via turbo (following rec in Staff Dashboard - External Form Upload: Display import summary / errors #1112), and the page doesn't reload, so I believe placing it right by the control that the user just interacted with would make it more visible.
• A red banner is shown for an error state, and a green banner is shown for a success state.
• I set a role="alert" on the heading of the dynamically injected content, so that assistive technology users, such as screen reader users, are made aware of this new content via announcement when it's added to the page.

📷 Screenshots/Demos

[jmilljr24]

@khiga8 Thanks for pointing this out! This started a discussion in our last meeting about other validations we should be checking for in this service. I opened PR #1211 which adds a file type validation and checks for the correct headers.

Hopefully I didn't step on your toes, but I figured the validations were outside the scope of this issues and didn't want to cause any confusion or add more work. If you have a better way to validate though I'd love to see it!!

[khiga8]

This is great! Thank you :)