Add `--` in some commands that receive user input
and if interpreted as options could lead to remote
code execution (RCE).

There may be more commands that could benefit from `--`
so the input is never interpreted as an option,
but most of those aren't dangerous.

Fixed commands:

- push
- pull
- fetch
- clone/clone_from and friends
- archive (not sure if this one can be exploited, but it doesn't hurt
  adding `--` :))

For anyone using GitPython and exposing any of the GitPython methods to users,
make sure to always validate the input (like if starts with `--`).
And for anyone allowing users to pass arbitrary options, be aware
that some options may lead fo RCE, like `--exc`, `--upload-pack`,
`--receive-pack`, `--config` (gitpython-developers#1516).

Ref gitpython-developers#1517

Taken from gitpython-developers#1516