Have a way to gather stats about the exported data.
Users can now call `ExportOperation.GetStats()` at the end of the run to get the stats for the operations. The data will be in the format `map[path.CategoryType]data.KindStats` whre `KindStats` is:
```go
type KindStats struct {
BytesRead int64
ResourceCount int64
}
```
---
#### Does this PR need a docs update or release note?
- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No
#### Type of change
<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup
#### Issue(s)
<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* https://github.com/alcionai/corso/issues/4311
#### Test Plan
<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E
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