docs(admin): document encryption:clean-orphaned-keys occ command

[hamza221]

AI-assisted: Claude (claude-sonnet-4-6)

☑️ Resolves

*Ref nextcloud/server#56400 and nextcloud/server#55556

🖼️ Screenshots

[hamza221]

/backport to stable33

[hamza221]

/backport to stable32

[hamza221]

/backport to stable31

[backportbot]

The backport to stable31 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable31
git pull origin stable31
# Create the new backport branch
git checkout -b backport/14485/stable31
# Cherry pick the change from the commit sha1 of the change against the default branch# This might cause conflicts, resolve them
git cherry-pick 38b647f6
# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/14485/stable31

Error: Failed to check for changes with origin/stable31: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[backportbot]

The backport to stable32 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable32
git pull origin stable32
# Create the new backport branch
git checkout -b backport/14485/stable32
# Cherry pick the change from the commit sha1 of the change against the default branch# This might cause conflicts, resolve them
git cherry-pick 38b647f6
# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/14485/stable32

Error: Failed to check for changes with origin/stable32: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[backportbot]

The backport to stable33 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable33
git pull origin stable33
# Create the new backport branch
git checkout -b backport/14485/stable33
# Cherry pick the change from the commit sha1 of the change against the default branch# This might cause conflicts, resolve them
git cherry-pick 38b647f6
# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/14485/stable33

Error: Failed to check for changes with origin/stable33: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.