Update FolderEntry for size and modified time (#1851)

## Description

Update the `FolderEntry` type with placeholder fields for folder size and modified time values.

## Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [x] 🕐 Yes, but in a later PR
- [ ] ⛔ No 

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor

## Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #1850 

## Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

src/pkg/backup/details/details.go

@@ -283,6 +283,8 @@ func (i ItemInfo) infoType() ItemType {
 type FolderInfo struct {
 	ItemType    ItemType  `json:"itemType,omitempty"`
 	DisplayName string    `json:"displayName"`
+	Modified    time.Time `json:"modified,omitempty"`
+	Size        int64     `json:"size,omitempty"`
 }
 
 func (i FolderInfo) Headers() []string {