[Outlook] Freeze legacy outlook connector and document deprecation

## Parent

Part of #4264
Blocked by: design sub-issue (Phase 0)

## Summary

Freeze legacy `outlook` (no new features) and document deprecation of the EWS / `full_access_as_app` cloud path. Prefer docs + metadata over behavior changes.

## Scope

- Mark legacy `outlook` as deprecated in class metadata / docs as appropriate
- Add deprecation notes for `full_access_as_app` / EWS cloud usage
- Clarify legacy `outlook` remains for **existing** deployments only; new M365 work goes to `outlook_cloud`
- Kibana: prefer **hide from create flow** for legacy `outlook` on versions that ship the new connectors (#4357) — confirm in design (#4346)

## Acceptance criteria

- [ ] Deprecation is visible in code/docs for reviewers and users
- [ ] No functional sync path changes for existing `outlook` deployments
- [ ] Points users toward `outlook_cloud` / `exchange_server` once those exist

## Out of scope

- Removing EWS or `exchangelib`
- Auto-migrating existing connector configs

Start with the legacy `outlook` connector's class metadata and documentation, then review design sub-issue #4346 and the references to `outlook_cloud` and `exchange_server`. Done means deprecation is visible, existing `outlook` sync behavior is unchanged, and users are directed to the newer connectors without removing EWS or `exchangelib`.

Written by the indexing model from the issue text.