text: Title: 1.14: Fix incorrect procMount defaulting
  Body: **What this PR does / why we need it**:
  
  Fixes incorrect forcing of the alpha procMount field to a non-nil value.
  
  **Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
  xref #78633
  
  See similar discussion around impact of defaulting fields within pod spec on workload controllers in #69988 and #69445.
  
  **Special notes for your reviewer**:
  
  This PR restores the behavior for this alpha field to the way it was in 1.12 and 1.13, with one change: objects without the alpha field set are allowed to remain nil. This prevents unrelated updates to a workload object (like annotating it) from modifying the pod spec portion of the object and forcing a spurious rollout.
  
  This also updates the fixtures used in the workload upgrade tests that would have caught this issue.
  Similar changes are required in 1.12 and 1.13.
  
  **Release note**:
  ```release-note
  Resolves spurious rollouts of workload controllers when upgrading the API server, due to incorrect defaulting of an alpha procMount field in pods
  ```
  
  /sig apps
  /cc @janetkuo @smarterclayton
  /priority critical-urgent