Expose booster-dev from flake (#4335)

~Needs runtimeverification/haskell-backend#3856
~Blocked on
#4319 (review)

@PetarMax wants to experiment with Booster-only simplifications in
Kontrol. To avoid the need for power-users of Kontrol to building the
backend from source, we should expose booster-dev in flake.nix and also
forward it to K's flake, so that it is installed with kup install k.

flake.nix

@@ -114,6 +114,7 @@
             p.kore-rpc
             p.kore-rpc-booster
             p.kore-rpc-client
+            p.booster-dev
           ];
         };