Feature: Add testing exercises for RSpec lessons

[rlmoser99]

Because:

• The new RSpec testing lessons needs corresponding exercises.

This Commit:

• Adds 5 RSpec Matcher exercises for Testing Basics lesson.
• Adds 2 RSpec exercises for Testing Part 2 lesson.
• Updates RSpec version.
• Adds rubocop, but ignores the ruby_basics directory.
• Adds README for the ruby_testing directory.

Closes Exercises for RSpec Basics