Move implicit-hie logic into vscode-haskell

* https://github.com/haskell/haskell-language-server/blob/a7262964e00d65f79688825aafd77acb497c2c90/ghcide/session-loader/Development/IDE/Session.hs#L259
* https://hackage.haskell.org/package/implicit-hie-cradle-0.5.0.1/docs/src/Hie.Implicit.Cradle.html#loadImplicitHieCradle

I feel this is shady. It's better to move this into vscode-haskell, where we can prompt the user for a decision and then create `hie.yaml` for them.

HLS CI should have simple and predictable behavior. E.g. either use default cradle, always fall back to cabal or error out.