[Outlook] outlook_cloud: DLS + access control sync

[Jan-Kazlouski-elastic]

Parent

Part of #4264
Blocked by: Graph attachments

Summary

Port DLS / access-control sync to outlook_cloud with mailbox-level ACL decoration parity.

Scope

• Port _prefix_email / identity doc generation from Outlook utils.py
• Mailbox-level ACL decoration parity (_mailbox_access_control)
• Reuse DLS test patterns from test_outlook.py

Acceptance criteria

• Identity docs + content ACL decoration match dialect of legacy Outlook
• Email casing / reachability tests ported and green
• DLS toggle behaves like legacy

Out of scope

• Incremental sync