feat: Name and Tag of latest release in repository by URL

[yourneko]

The feature description

Using the link to GitHub repo, gets a name and a tag of a latest release.

Concerns

GitHubRelease request is not async, because UnityWebRequest is allowed to be created and to start exceptionally from the main thread. I don't know if there is some reasonable workaround for this limitation.
Adding a dependency on NewtonSoft.Json seemed unnecessary for finding 2 values in the json string, so for now I avoided it.

Test

To test the feature, you can use following script:

 public class TestRepoReleaseComponent : MonoBehaviour
 {
     [SerializeField] string RepoURL = @"https://api.github.com/repos/OneSignal/OneSignal-Unity-SDK/releases/latest";
     GitHubRelease m_Release;

     void Start ()
     {
         GitHubUtility.GetLatestRelease (RepoURL, release => Debug.LogError ($"tag {release.Tag}; version {release.Name}"));
     }
 }

[stan-osipov]

Please document public API points.