Automatic merge from submit-queue (batch tested with PRs 43016, 50503, 51281, 51518, 51582). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>..
Refactor: Moving disk-related cloud provider operations to gce_disks.go
**What this PR does / why we need it**: The main GCE cloud provider code (pkg/cloudprovider/providers/gce/gce.go) should not contain disk-related operations. Moved them to gce_disks.go
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes#51280
**Release note**:
```release-note
NONE
```
/release-note-none
/sig storage
/assign @msau42 @bowei
55798b265c