Allow pushing branches to forks

**Describe the solution you'd like**
I contribute to various repositories where the development model involves forking a repo, pushing to the fork, and then making a PR back to the parent repo. In this situation my forked repo's main branch is rarely up-to-date because the local main branch is pointing to the parent repo's version of the branch, i.e. locally I have `main -> upstream/main` and `origin/main` lags arbitrarily far behind `upstream/main`. In those scenarios, I would like to be able to point git-xargs to push my new branch to a different repo than the repository from which it was cloned. I envision something like:

```
git-xargs \
--branch-name test-branch \
--repo parent/repo \
--push-repo forked/repo \
--commit-message "Create hello-world.txt" \
touch hello-world.txt
```

Apologies in advance if there's a way to do this that I'm missing! I've read through the README and glanced through issues, and don't see anything similar discussed anywhere.

**Describe alternatives you've considered**
Keeping the main branch on my forks would partially address this problem by ensuring that I am making changes from the same state as the parent repo. However, you would still need a way for the created PRs to point back to the parent repo rather than the main branch on the fork, which IIUC requires some additional information no matter what.

**Additional context**
None