fix(ui): inconsistent pill sizes across admin panel (#12788)

### What?
Fixes inconsistent `pill` sizes across the Admin Panel.

### How?
Pills without a specified size default to **medium**. In the folders
[PR](https://github.com/payloadcms/payload/pull/10030), additional
padding was to the medium size. As a result, any pills without an
explicit size now appear larger than intended.

This PR fixes that by updating any pills that should be small to
explicitly set `size="small"`.

Fixes #12752

packages/ui/src/elements/BulkUpload/FileSidebar/index.tsx

@@ -92,6 +92,7 @@ export function FileSidebar() {
               <Pill
                 className={`${baseClass}__header__addFile`}
                 onClick={() => openModal(addMoreFilesDrawerSlug)}
+                size="small"
               >
                 {t('upload:addFile')}
               </Pill>