Allow rebasing with comitter date as author date

**Is your feature request related to a problem? Please describe.**
Rebasing branches is a prevalent part of my workflow. To avoid mangling dates during this, I always rebase with the `--committer-date-is-author-date` flag to preserve the original date of the commit when viewed in GitHub, BitBucket, or any other application that shows the committer date instead of the author date. As far as I can tell, Lazygit has no way to set this flag globally for all rebase operations.

**Describe the solution you'd like**
A config option to set this flag automatically when doing any type of rebase.

**Describe alternatives you've considered**
- Rebasing outside of Lazygit.
- Do complex interactive rebases within Lazygit, then go back and rebase again manually with the flag to fix the dates (when it is reasonable to do so).

**Additional context**
The `--committer-date-is-author-date` flag implies `--force-rebase`, which may not always be desired. I suppose ideally it'd only be applied if the operation would actually change the committer date, but I'm not sure how Git handles dates when fast-forwarding to know if that's necessary, or if it's feasible to implement.