feat: emitting an event when handling a client upgrade proposal (back…

…port cosmos#1570) (cosmos#1594)

* feat: emitting an event when handling a client upgrade proposal (cosmos#1570)

* feat: emitting an event when handling a client upgrade proposal

* refactor: only emit event if err is nil

* refactor: idiotmatic go:

(cherry picked from commit 8422d0c)

* Update CHANGELOG.md

Co-authored-by: Sean King <seantking@users.noreply.github.com>