Allow providing custom path to .tool-versions file to look at

[mkaput]

Problem

One of our users has a Scarb project in a submodule/subdirectory of the repository. This project contains a .tool-versions file that the user wants to use as reference point for version selection, but there is no way to instruct the action to look for this file elsewhere than the working directory.

Proposed Solution

Add a new input, named tool-versions, typed as an optional string. It will accept a path, absolute or relative to action's PWD, to the tool-versions file, that must exist. If provided, the action will always and only look for Scarb version in that provided path. No other deduction techniques will be applied, and inability to look for information should yield an error.

Example:

- uses: software-mansion/setup-scarb@v1
  with:
    tool-versions: ./my-submodule/.tool-versions

Notes

Most of the meat lies in this file: https://github.com/software-mansion/setup-scarb/blob/67ef98b555967b95dd7fc56ecdd1e93ce7cefdae/lib/versions.js. It is called from here:

setup-scarb/lib/main.js

Lines 15 to 22 in 67ef98b

	const scarbVersionInput = core.getInput("scarb-version");
	const { repo: scarbRepo, version: scarbVersion } = await determineVersion(
	scarbVersionInput,
	{
	repo: "software-mansion/scarb",
	nightliesRepo: "software-mansion/scarb-nightlies",
	},
	);

[EvolveArt]

I'm on it 🫡

[mkaput]

Please don't forget about adding a test in our CI workflow, and also documenting this field in the readme 😃 Many thanks 😍