RFE: allow (ghc with) missing haddock

### General summary

I sometimes build ghc locally without haddock to save time.
It would be nice if it was possible to use stack with such a ghc.

### Steps to reproduce

1. Remove (or "disable") haddock (or switch to a ghc without haddock enabled)
2. Run command `stack install`.

### Expected
stack to ignore missing haddock binary since it is not needed for `stack install`.

### Actual

```shellsession
$ stack-2.9.3 install
Trouble loading CompilerPaths cache: CompilerFileMetadataMismatch
Error: [S-2476]
Found an invalid compiler at "/var/home/petersen/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7/bin/ghc": Error: [S-4764]
Could not find any of: ["/var/home/petersen/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7/bin/haddock","/var/home/petersen/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7/bin/haddock-ghc"]
```

### Stack version

```shellsession
$ stack --version
Version 2.9.3, Git revision 6cf638947a863f49857f9cfbf72a38a48b183e7e x86_64 hpack-0.35.1
```

### Method of installation

* Official binary, downloaded via haskellstack.org or from Stack's repository (via stack upgrade)

### Platform
Fedora Linux