Add new RSpec/Rails/HaveHttpStatus cop

[akiomik]

This cop checks that tests use have_http_status instead of equality matchers (e.g. be).

Example

# bad
expect(response.status).to be 200

# good
expect(response).to have_http_status 200

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• Added the new cop to config/default.yml.
• The cop is configured as Enabled: pending in config/default.yml.
• The cop is configured as Enabled: true in .rubocop.yml.
• The cop documents examples of good and bad code.
• The tests assert both that bad code is reported and that good code is not reported.
• Set VersionAdded in default/config.yml to the next minor version.

If you have modified an existing cop's configuration options:

• Set VersionChanged in config/default.yml to the next major version.

[pirj]

Looks good!
Just glanced over, let me run it on real-world-rspec later today.

[pirj]

Checked on real-world-rspec:

57497 files inspected, 3841 offenses detected, 3841 offenses auto-correctable

and all those thousands of offences look legit! 👏 🎉

Thank you! Fantastic contribution!