git_command: Augment underlying git errors with suggestions

This change appends suggestions to the underlying git error to make the
error slightly more actionable.

DD: go/improve-repo-error-reporting & go/tee-repo-stderr

Bug: b/292704435
Change-Id: I2bf8bea5fca42c6a9acd2fadc70f58f22456e027
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/387774
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
Reviewed-by: Jason Chang <jasonnc@google.com>
Tested-by: Aravind Vasudevan <aravindvasudev@google.com>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>

project.py

@@ -1135,7 +1135,7 @@ class Project(object):
         url = branch.remote.ReviewUrl(self.UserEmail, validate_certs)
         if url is None:
             raise UploadError("review not configured", project=self.name)
-        cmd = ["push"]
+        cmd = ["push", "--progress"]
         if dryrun:
             cmd.append("-n")