Pass DocsUI owner to alexbn@

I'll be away for some time, pass the owner to Alex to make sure
we still have reviews in APAC to handle code review load shedding.

Bug: None
Test: None
Flag: EXEMPT OWNERS change
(cherry picked from https://android-review.googlesource.com/q/commit:9abde6c9f8be8aae8569a5d3fa6e312d3944ee14)
Merged-In: I5cd8c94ade77b33f268270a17f5d3a058d671ea9
Change-Id: I5cd8c94ade77b33f268270a17f5d3a058d671ea9