Support for modpacks

[RobinVanCauter]

I've been trying to use Lodestone for some of my servers, but ran into the following issue:

Upon creation of a new instance, lodestone asks which flavour to use: vanilla / fabric / forge and then download and installs the latest version of these mod managers. The problem is, most of the large and popular modpacks are not built to be used with the latest version of these modloaders, they usually lag a couple of versions behind. As a result, I think nearly any server trying to use fabric or forge with existing modpacks, are not well supported at the moment.

For example, when I pick forge, remove the "by lodestone installed" forge files (as it won't work with the newest version), then copy over all of the files from a modpack it's server pack, I get the following error:

Error: could not open `C:\Users\Administrator\.lodestone\instances\Create Test-c6521e1d\libraries\net\minecraftforge\forge\1.19.2-43.2.6\win_args.txt'

There's a couple of different solutions that would fix this problem:

• Allow changing the command or executable used to run an instance (much like being able to pass custom args)
• Allow picking a specific forge/fabric/,, version on instance creation

Thanks for all the hard work, love the design, love the tech stack!