Add --cabal-plan

ghcup.cabal

@@ -186,9 +186,12 @@ executable ghcup
     -fwarn-incomplete-record-updates -threaded
 
   build-depends:
+    , aeson                 >=1.4      && <1.6
+    , aeson-pretty          ^>=0.8.8
     , async                 ^>=2.2.3
     , base                  >=4.13     && <5
     , bytestring            ^>=0.10
+    , cabal-plan            ^>=0.7.2
     , containers            ^>=0.6
     , deepseq               ^>=1.4
     , filepath              ^>=1.4.2.1