[tools] rename `--username` argument to `--owner`
[tools] rename `--username` argument to `--owner`

The release devtool command requires `--username` argument
to be passed to specify the GitHub owner of the repo we want
to push the tag to. Because this can be confusing, this commit
changes the cli argument from `--username` to `--owner`.

Signed-off-by: Luminita Voicu <6c9c51795b037b189e54c262e37c535895f48539@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker