Add hackerrank and hackerearth as one of the site options

We need to cover as many sites and possible. [Hackerrank](https://www.hackerrank.com/) and [Hackerearth](https://www.hackerearth.com/) being one of the most popular ones should be added. Also, their rating colors should be researched first.

Look at how existing sites like CodeChef and Codeforces are integrated in the codebase, likely in a file handling API calls or rating logic. Research the public APIs or rating color schemes for Hackerrank and Hackerearth. Implement new site handlers following the existing pattern, then test by generating an image with a sample handle.

索引モデルが issue の本文から書いたものです。