Add `faraday-http-cache` gem for Octokit caching

What does this MR do and why?

As per octokit#caching README, we're adding caching for our octokit.rb configuration. It should help us with:

• boosting the performance,
• stretching our API rate limit,
• avoiding paying the hypermedia tax.

Add faraday-http-cache gem for Octokit caching

Changelog: performance

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Access the Rails console rails c
2. Initialize new Octokit client, e.g.: client = Octokit::Client.new(:access_token => token)
3. Make some requests, e.g.: client.user
4. Repeat the same request, and validate that the request has been cached.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.