Add branch to .gitmodule + bump to bbf11bb

This allows you to run `git submodule update --remote` to bump to the
latest commit on that branch.

.gitmodules

 [submodule "proxy/translation"]
 	path = proxy/translation
 	url = https://git.torproject.org/translation.git
+	branch = snowflakeaddon-messages.json_completed

translation @ bbf11bb0

-Subproject commit 75d3b037adf2041b772265e7c1d4e7b3091bc5b8
+Subproject commit bbf11bb0c9f1aca4f6b18c6505645f85e2fa1986