docs: remove documentation for archived apps

[DeepDiver1975]

The impersonate and sharepoint apps have been archived for security reasons and are no longer maintained. This removes their documentation footprint:

• Delete the dedicated pages: configuration/general_topics/impersonate_users.adoc, enterprise/external_storage/sharepoint-integration_configuration.adoc, classic_ui/external_storage/sharepoint_connecting.adoc.
• Remove all inbound navigation and xref references (admin_manual + classic_ui nav, general-topics index, occ config-commands cross-reference).
• Drop both entries from the supported-apps list.
• Reword the file-lifecycle and Kiteworks-migration passages that recommended installing the Impersonate app.

Historical release notes are intentionally left untouched. The updater and direct_menu apps have no dedicated documentation. Generic/unrelated "impersonate" references (audit-log events, oCIS auth-app impersonation, security prose) are preserved.

[mmattel]

Q, without having that checked manually, are the impersonate and sharepoint apps removed from the image already? The text above does not mention this.

[DeepDiver1975]

LGTM overall — clean removal, no dangling xrefs, both apps verified archived (owncloud/impersonate and owncloud/sharepoint, isArchived: true).

Verified against PR head:

• No remaining xref:/nav reference to any of the 3 deleted pages (impersonate_users.adoc, sharepoint-integration_configuration.adoc, sharepoint_connecting.adoc) → Antora build won't break.
• Supported-apps list, both nav files, general-topics index, and _config_commands.adoc cross-ref all cleaned. Reworded files_lifecycle.adoc TIP and migrating_to_kiteworks.adoc passages read cleanly (no dangling list markers, grammar intact).
• Remaining "sharepoint" mentions are unrelated (prose in classic_ui/.../sharing.adoc, external MS-docs URLs) — correctly left alone.

Nit (non-blocking, no build impact):

• Orphaned image dirs left behind — their only consumers were the deleted pages:
  • modules/admin_manual/images/apps/impersonate/ (6 PNGs)
  • modules/admin_manual/images/enterprise/external_storage/sharepoint/ (4 PNGs)
    No .adoc references them anymore. Antora ignores unused images so the build is fine; delete them in this PR for completeness or leave for a follow-up.

changelog=n-a (docs repo has no changelog).

🤖 Generated with Claude Code

[mmattel]

I will take care on orphaned images. There is an easy process for that. A extension I have written needs to be enabled for this and prints orphaned files that can post reviewing be removed.

Done, will be fixed with the upcoming additional changes:

[11:20:43.699] WARN (find-orphaned-objects): Start finding orphaned files


# server next 

modules/admin_manual/images/apps/impersonate/impersonate_enable.png
modules/admin_manual/images/apps/impersonate/impersonate_group_admins_only.png
modules/admin_manual/images/apps/impersonate/impersonate_groups_only.png
modules/admin_manual/images/apps/impersonate/impersonate_oc_admins_only.png
modules/admin_manual/images/apps/impersonate/impersonating-a-user.png
modules/admin_manual/images/apps/impersonate/picking-a-user-to-impersonate.png
modules/admin_manual/images/enterprise/external_storage/sharepoint/sharepoint-1.png
modules/admin_manual/images/enterprise/external_storage/sharepoint/sharepoint-2.png
modules/admin_manual/images/enterprise/external_storage/sharepoint/sharepoint-3.png
modules/admin_manual/images/enterprise/external_storage/sharepoint/sharepoint-4.png


[11:20:43.809] WARN (find-orphaned-objects): End finding orphaned files
[11:20:43.810] WARN (find-orphaned-objects): Stopping build process by config