Support rsync executable override per profile

[sohoffice]

I stumbled upon an interesting use case. I synced from my Macbook to a Windows VM. However, I find myself wanted to sync from this windows VM to a second location. The windows VM require wsl rsync to work, but my host doesn't. Obviously, a single executable section in the top-most level of piaasconfig.yml is not enough. The scenario looks like the below:

Host ---> Windows ---> 2nd Windows

It would be nice if we can override executable per profile.