Restrict MSGraph deferrable pagination to the configured host - #71842

This PR addresses a genuine CWE-918 (SSRF) risk: when MSGraphAsyncOperator.trigger_next_link() fires a new MSGraphTrigger for the next page, the url comes directly from the previous API response's @odata.nextLink. Without a host check the Kiota adapter would attach the bearer token to whatever host the response contained.

The approach — adding pagination_link: bool to the trigger, propagating it through serialize(), and calling a centralised assert_allowed_host() before the request — is clean and correct for the trigger path.

Two points worth addressing before merge:

1. Configurability gap (inline comment on hooks/msgraph.py): the single-endpoint check is correct for normal use (SharePoint/Power BI callers configure host to match, so pagination links pass). The gap is when a caller passes an absolute url that differs from the connection’s host, or uses a custom pagination_function returning absolute URLs for a different target. Making allowed_netlocs an explicit opt-in set fixes this at no security cost. The reviewer has working local code; a ready-to-use snippet is in the inline comment.

2. Test isolation (inline comment on test_msgraph.py): test_pagination_refuses_cross_host_next_link validates the full end-to-end path but hides the exception-wrapping mechanics. A direct unit test of assert_allowed_host() on the hook would make the contract explicit and survive any future changes to the trigger’s exception handler.

The nit on hooks/msgraph.py is a minor refactoring suggestion (making the check synchronous) that follows naturally if point 1 is adopted.

Drafted-by: Claude Sonnet 4.6 (claude-sonnet-4.6); reviewed by @dabla before posting