Automatic merge from submit-queue (batch tested with PRs 51235, 50819, 51274, 50972, 50504)
Changing scheduling part to manage one single local storage resource
**What this PR does / why we need it**:
Finally decided to manage a single local storage resource
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: part of #50818
**Special notes for your reviewer**:
Since finally decided to manage a single local storage resource, remove overlay related code in scheduling part and change the name scratch to ephemeral storage.
**Release note**:
```release-note
Changing scheduling part of the alpha feature 'LocalStorageCapacityIsolation' to manage one single local ephemeral storage resource
```
/assign @jingxu97
cc @ddysher
e923f2ba5c