Allow me to update rows by id when uploading csv files

**Is your feature request related to a problem? Please describe.**
I prefer using dolthub instead of cloning a repo to my local dolt to perform PR's to bounties. This is because all that data is hard to deal with in a local repo.
One of the issues with this is most dolt features aren't avaible directly on dolthub. One in particular is updating rows.

**Describe the solution you'd like**
Dolthub has 3 options when uploading a csv file to a table: Update, Replace and Overwrite.

Update is more like an "Add to" instead of update. Instead, I would like update to have suboptions when it detects key conflicts. Say my files has keys already in the database, I would like to be able to only replace those fields or not replace those fields. It would work as an actual update without needing SQL queries to update specific rows.

**Describe alternatives you've considered**
Creating separate branches or recreating the repository, too much work tho :P

**Additional context**
This is related to file upload on dolthub.