IWYU: Add missing include for std::optional usage in desktop_view_manager_interface.h

In the CL https://crrev.com/c/6576162 used std::optional in the
chrome/browser/privacy_sandbox/notice/desktop_view_manager_interface.h,
but corresponding include was missed.
Added missing include for std::optional usage.

Bug: 41455655
Change-Id: Ia9e0f95a6557e6a1d5af781032022b63b99901f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6780629
Reviewed-by: Abe Boujane <boujane@google.com>
Commit-Queue: Fiona Macintosh <fmacintosh@google.com>
Reviewed-by: Fiona Macintosh <fmacintosh@google.com>
Cr-Commit-Position: refs/heads/main@{#1491380}