Support installing crates using Git URLs

[mandrean]

Do the checklist before filing an issue:

• [x] Is this related to the actions-rs Actions? If you think it's a problem related to Github Actions in general, use GitHub Community forum instead: https://github.community
• [x] You've read the Contributing section about feature requests: https://github.com/actions-rs/.github/blob/master/CONTRIBUTING.md#feature-requests
• [x] Is this something you can debug and fix? Send a pull request! Bug fixes and documentation fixes are welcome.

Motivation

As an action-rs/install user, it would be useful to have the ability to also install crates using Git URLs, and not just crates published on crates.io.

Also it would match the actual cargo install command better, since it has the --git/--branch/--tag/--rev flags precisely for this purpose.

One use-case for example is old, unmaintained crates with a new fork that doesn't have its own published crate.

Workflow example

- uses: actions-rs/[email protected]
  with:
    crate: cargo-audit
    version: latest
    git: https://github.com/RustSec/cargo-audit
    use-tool-cache: true

- uses: actions-rs/[email protected]
  with:
    crate: cargo-audit
    version: latest
    git:
      repo: https://github.com/RustSec/cargo-audit
      branch: master
      tag: v0.12.1
      # rev: d3017c3
    use-tool-cache: true