Change the install name of flyctl to fly

[offbyone]

Per the README in the flyctl repo:

Note: Most installations of flyctl also alias flyctl to fly as a command name and this will become the default name in the future.

https://github.com/superfly/flyctl/blob/master/README.md?plain=1#L5-L6

Alternately, I could alias them; it's up to you, if you prefer one or
the other.

[chessmango]

Thanks for the contribution!
That said, I'm not sure I'm a fan of outright switching to fly considering flyctl is still acceptable.
I've aliased things for now myself, mostly thinking that when the actual binary name changes or flyctl is considered fully deprecated, I'll go ahead and change things around - or at least allow versions on either side of that deprecation to be installed still. :)

[chessmango]

I'm gently looking at including the same as fly so behaviour is similar to other packages, though I haven't yet tried to ship multiple binaries or shims via asdf :D