[FEATURE] Offer to lauch a merge tool when throwing error beacuse target contents were changed

[desk7]

Is your feature request related to a problem? Please describe.
Git often delete the symlink to .gitconfig and replace it with a new .gitconfig when changing settings. So when I dotter-deploy, I often receive the error

[ERROR] Updating template ".gitconfig" -> "C:\\Users\\USER/.gitconfig" but target contents were changed. Skipping
[ERROR] Some files were skipped. To ignore errors and overwrite unexpected target files, use the --force flag.

I'm always frustrated because I have to manually open the source file and the target file in winmerge to solve the conflict and then I can deploy.

Describe the solution you'd like
I'd like dotter to offer me the possibility to launch a custom merge tool (also the git default one) that opens the two files and let me rapidly resolve the conflict, saving the changes in the source file.