[native] Add message search context

Summary:
issue: https://linear.app/comm/issue/ENG-3163/create-the-search-screen-for-message-searching
Since the query has to be passed between the search screen and the header component, that is passed in screen options, I created a context to hold the query

Test Plan: tested with next diffs

Reviewers: kuba, kamil, bartek

Reviewed By: kamil, bartek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7739