Add `mc license register` command to replace `mc support register`

[ravindk89]

As per https://github.com/minio/mc/commit/603857371c31dacacb0f79701ca6c451c0ade9a5 and the July 29th release, mc support register is deprecated in favor of mc license register.

Server must match or be near client version for this to work.

Should be enough to rename and global find/replace on the string.