Enhancement request: git-push: Allow (configurable) default push-option

[Marius Paliga]

There is a need to pass predefined push-option during "git push"
without need to specify it explicitly.

In another words we need to have a new "git config" variable to
specify string that will be automatically passed as "--push-option"
when pushing to remote.

Something like the following:

git config push.optionDefault AllowMultipleCommits

and then command
  git push
would silently run
  git push --push-option "AllowMultipleCommits"