Update repo & references for "Kuzzle Backend"

[appacea]

Update all references and repos to match product name.

For example for "Kuzzle Backend", repo should be:

https://github.com/kuzzleio/kuzzlebackend.git

And links such as this one need to be updated:

https://github.com/kuzzleio/documentation/blame/62427cea4c3a135b5b961a2b6c8d94f02b7fca5f/src/guide/essentials/installing-kuzzle.md#L136