fix(ui): better responsiveness for upload fields in sidebar (#8101)

## Description

Adjusts the styling for the Dropzone component for upload fields with
`admin.position: sidebar`.

Before:
![Screenshot 2024-09-06 at 4 10
28 PM](https://github.com/user-attachments/assets/221d43f9-f426-4a44-ba58-29123050c775)

After:
![Screenshot 2024-09-06 at 4 09
32 PM](https://github.com/user-attachments/assets/c4369a65-d842-4e65-9153-19244fcf5600)


- [x] I have read and understand the
[CONTRIBUTING.md](https://github.com/payloadcms/payload/blob/main/CONTRIBUTING.md)
document in this repository.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] Existing test suite passes locally with my changes
- [ ] I have made corresponding changes to the documentation

Author: tylandavis

packages/ui/src/elements/Upload/index.scss

@@ -91,6 +91,8 @@
 
   &__dropzoneContent {
     display: flex;
+    flex-wrap: wrap;
+    gap: base(0.4);
     justify-content: space-between;
     width: 100%;
   }
@@ -106,6 +108,7 @@
   }
 
   &__dragAndDropText {
+    flex-shrink: 0;
     margin: 0;
     text-transform: lowercase;
     align-self: center;

packages/ui/src/fields/Upload/index.scss

@@ -9,6 +9,8 @@
 
   &__dropzoneContent {
     display: flex;
+    flex-wrap: wrap;
+    gap: base(0.4);
     justify-content: space-between;
     width: 100%;
   }
@@ -34,6 +36,7 @@
   }
 
   &__dragAndDropText {
+    flex-shrink: 0;
     margin: 0;
     text-transform: lowercase;
     align-self: center;