Move spdk-rs to the mayastor repo

[tiagolobocastro]

Is your feature request related to a problem? Please describe. Move spdk-rs repo to the mayastor repo. In practice only mayastor seems to really use this repo. Moving them together will simplify the management, especially considering that now the rust compiler environment etc is defined on this repo and therefore adds the extra burden of modifying this repo first, and then resync mayastor. Also it's not uncommon to have more than 1 crates on the same repo, it might make cloning a little slower though, but that is something you don't do a lot anyway.

Describe alternatives you've considered Leave as is.

Additional context Not that there aren't good reasons to keep it separate, but it's not without the downside of tiresome resyncs time and time again...