Installed stack overrides 'compiler-version' that is set in `stack.yaml` of project

I have attempted to install Miso, which uses GHCJS. ([installation instructions](https://github.com/dmjio/miso#stack); I followed the 'stack' instructions)

Currently, installing GHCJS through asdf-haskell is not possible. However, it will also simply override the configured compiler version that is set in the project's `stack.yaml` with the one in the `.tool-versions`.

Since there is no way to override or turn off this behaviour, I had to uninstall asdf-haskell, and manage Haskell-versions outside of asdf.

It would really help if GHCJS and similar compilers were installable through `asdf-haskell`, and if the warning message that is used when the compiler version of the `stack.yaml` is present but discarded could be improved.

Start with the installation instructions and inspect how the plugin handles the compiler version in the project's stack.yaml versus .tool-versions. Trace the warning shown when stack.yaml is discarded and determine the existing installation path for GHCJS or similar compilers. Done means GHCJS can be installed through asdf-haskell, the configured version can be preserved or intentionally overridden, and the warning clearly explains the behavior.

Written by the indexing model from the issue text.