Hide GHCi message about ghci.conf being loaded

Summary

Have a flag to make GHCi not output the string "Loaded GHCi configuration from path/to/ghci.conf". This would let the ghci.conf file be in complete charge of what is displayed, instead of being necessarily followed by that string. (This is for cosmetic reason, e.g. when demoing GHCi or providing a specific configuration that displays instructions to follow.)

I think the same option should also hide the version string (but this version string is displayed before the ghci.conf file acts, so ghci.conf can e.g. clear the clear, and thus is a bit less inconvenient).

Steps to reproduce

Make sure a ghci.conf file exists (it can be empty), then use it with the -ghci-script option.

$ touch ghci.conf
$ _build/stage1/bin/ghc --interactive -ghci-script ghci.conf

Current behavior

$ _build/stage1/bin/ghc --interactive -ghci-script ghci.conf
GHCi, version 9.11.20240322: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from ghci.conf
ghci>