Copy SecurityContext from Containers[0] if present for PVR

[sseago]

Thank you for contributing to Velero!

Please add a summary of your change

Velero 1.15.1 added a change to set a default SecurityContext on the fs-backup InitContainer to fix a bug related to pod security standards enforcement. In an OpenShift environment, when the pod was created by a non-admin user, using this default SecurityContext with runAsUser set based on the current (velero) user breaks because this forces the openshift.io/scc annotation to the default privileged level of the velero SA.

The fix is to use the SecurityContext from the first pod container if that container has a SecurityContext set, using the default otherwise.

Does your change fix a particular issue?

Fixes #8711

Please indicate you've done the following:

• [x ] Accepted the DCO. Commits without the DCO will delay acceptance.
• [x ] Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• [x ] Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.

Project coverage is 59.46%. Comparing base (e64806a) to head (21db5f8).
Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/restore/actions/pod_volume_restore_action.go	69.23%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8712      +/-   ##
==========================================
- Coverage   59.48%   59.46%   -0.03%     
==========================================
  Files         371      371              
  Lines       40191    40199       +8     
==========================================
- Hits        23909    23905       -4     
- Misses      14789    14799      +10     
- Partials     1493     1495       +2     

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[reasonerjt]

The log message printed in line 165 could be misleading, maybe just remove "Using default securityContext values" in the sentence?

[reasonerjt]

@sseago This change makes sense to me, is it convenient to add a UT?

[sseago]

@reasonerjt unit test added