Add codereview.cfg

Enables usage of git-codereview in this repo, which may be useful to
non-IntelliJ users.

See https://pkg.go.dev/golang.org/x/review/git-codereview#hdr-Configuration

Change-Id: If9ec6eae678c54bad86b126f9b9284b1a9c7ddd9

codereview.cfg

@@ -0,0 +1,3 @@
+gerrit: https://forge.certus.one
+issuerepo: certusone/wormhole
+branch: main