Closes #18990: Add description field to ImageAttachment model

[jeremystretch]

Closes: #18990

• Add an optional description field to the ImageAttachment model
• Enable global search for image attachments by name & description
• Establish a dedicated UI view for an image attachment to display all attributes

[arthanson]

This all works and potentially an existing issue but the detail view shown after you add an image is great, but is only accessible when you add an image. There is no way to get back to it from either the sub-table (like on a device) or from the main Image Attachment list view, maybe have the name field link to the detail view?

[jeremystretch]

Yeah, I went a little outside the scope of the FR honestly, and didn't want to push too far. I'm planning on doing some additional cleanup under #18204, which I expect to include linking to the detail view for individual image attachments.