[git_trace2] Add logs for critical cmds

Trace logs emitted from repo are not useful on error for many critical
commands. This change adds errors for critical commands to trace logs.

Change-Id: Ideb9358bee31e540bd84a94327a09ff9b0246a77
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/373814
Reviewed-by: Joanna Wang <jojwang@google.com>
Tested-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

subcmds/upload.py

@@ -657,6 +657,7 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
 
                 branch.uploaded = True
             except UploadError as e:
+                self.git_event_log.ErrorEvent("upload error: " + str(e))
                 branch.error = e
                 branch.uploaded = False
                 have_errors = True