Add support for version wildcards to git-based alternative cargo registries

[Veetaha]

At the time of this writing, #15 (comment) was implemented without the support for version wildcards. Users must pin a specific package version to use this action with an alternative cargo registry.

This issue was created based on the comment #15 (comment) which suggests downloading the git registry index to figure out the available versions of the package and match the version selector against that index.

The outcome of this issue is that it should be possible to use a semver wildcard in the version input of the action together with any registry and index parameters for non-crates-io registries.