[Outlook] Documentation + migration guide (outlook → outlook_cloud)

[Jan-Kazlouski-elastic]

Parent

Part of #4264
Blocked by: Kibana native connectors (and feature-complete connectors)

Summary

Update Elastic docs for the connector split: Graph permissions for outlook_cloud, EWS/LDAP for exchange_server, and a migration guide from legacy outlook.

Scope

• Update https://www.elastic.co/docs/reference/search-connectors/es-connectors-outlook (and/or split pages)
• Document Graph app permissions + Application Access Policy for scoped mailboxes
• Migration steps: create new connector, full resync expectation (_id change), permission changes
• Remove/replace full_access_as_app as the recommended cloud setup

Acceptance criteria

• Docs publish path clear (PR links)
• Migration guide covers resync + permissions
• full_access_as_app no longer presented as the forward-looking cloud path

Out of scope

• Code changes beyond docs references if any