Add --upstream option to branch

[timsehn]

The recommended way in Git to add a remote tracking branch to a checked out branch is:

$ git branch --upstream origin/branch

This option does not exist in Dolt. You can only set a tracking branch when you create a branch.

$ dolt branch --upstream origin/b1   
NAME
	dolt branch - List, create, or delete branches

SYNOPSIS
...
...
error: unknown option `upstream'

This also doesn't work:

$ dolt branch --track origin/b1
* b1                                            	
  main