Cannot `Cthulhu.save_config!()` if (previously saved) LocalPreferences.toml exists

[wheeheee]

I get the error e.g. if optimize is set to true in the existing config.

julia> Cthulhu.save_config!()
ERROR: ArgumentError: Cannot set preference 'optimize' to 'false' for Cthulhu in q:\DSP.jl\LocalPreferences.toml: preference already set to 'true'!
Stacktrace:
  [1] set_preferences!(::String, ::String, ::Pair{String, Bool}, ::Vararg{Pair{String}}; force::Bool)
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:153
  [2] set_preferences!(::String, ::String, ::Pair{String, Bool}, ::Vararg{Pair{String}})
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:131
  [3] set_preferences!(::Tuple{…}, ::Pair{…}, ::Vararg{…}; export_prefs::Bool, active_project_only::Bool, project_toml::String, kwargs::@Kwargs{})
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:292
  [4] set_preferences!(::Base.UUID, ::Pair{…}, ::Vararg{…}; export_prefs::Bool, active_project_only::Bool, project_toml::String, kwargs::@Kwargs{})
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:322
  [5] set_preferences!(::Base.UUID, ::Pair{String, Bool}, ::Pair{String, Vector{String}}, ::Vararg{Pair{String}})
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:294
  [6] set_preferences!(::Module, ::Pair{String, Bool}, ::Vararg{Pair{String}}; kwargs::@Kwargs{})
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:329
  [7] set_preferences!(::Module, ::Pair{String, Bool}, ::Pair{String, Vector{String}}, ::Vararg{Pair{String}})
    @ Preferences Q:\.julia\packages\Preferences\x9wI6\src\Preferences.jl:328
  [8] top-level scope
    @ Q:\.julia\packages\Cthulhu\keAhQ\src\preferences.jl:26
  [9] top-level scope
    @ Q:\.julia\packages\Cthulhu\keAhQ\src\preferences.jl:26
 [10] top-level scope
    @ REPL[10]:1
Some type information was truncated. Use `show(err)` to see complete types.```

[aviatesk]

We should probably need to specify force = true option.

[wheeheee]

or maybe overwrite=true

[serenity4]

I went with whatever Preferences.jl uses in #680, which will then be force = true (although I would otherwise have slightly preferred overwrite = true but I would say consistency is more important in this case).