Automatic merge from submit-queue (batch tested with PRs 48911, 49475, 49438, 49362, 49274)
set RBD default values as constant vars
**What this PR does / why we need it**:
When working on #49225, I found some [default RBD parameters](https://kubernetes.io/docs/concepts/storage/persistent-volumes/#ceph-rbd) had not been declared as constant values, which will be error-prone.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
set RBD default values as constant vars
```
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