Add `--overwrite-ignore` and `--no-overwrite-ignore` to `dolt checkout`

[elianddb]

Dolt checkout now overwrites ignored tables when switching branches by default, matching Git.

Add explicit flags so users can control this: --overwrite-ignore to overwrite ignored tables (and make the default explicit) and --no-overwrite-ignore to abort when the target branch would overwrite ignored tables. Mirror the behavior described in git-checkout(1) for these options.