Add search_engine parameter to Users endpoint + tests

[joshcanhelp]

• Replace the hard-coded search engine version v2 with a modifiable one
• Improve docs for the method
• Add unit and integration tests
• Remove skipped user test

[machuga]

LGTM

[machuga]

Nothing you need to worry about now since the convention is used, but just using as an opportunity to share info:

.fetch is typically used on a hash when you want to look for a key and raise an exception if it is not empty, or return a specific default. Accessing a hash key via the [] method is equivalent to .fetch(key, :nil), so when nil is the desired default return value, you'll typically find the [] method is used.

[joshcanhelp]

@machuga - So something like:

request_params = {
  ...
  q: [:q]
  ...
}

?

[machuga]

Close:

options[:key] === options.fetch(:key, nil)