Enable documentation feedback links

[nrichers]

Add documentation feedback link, like a thumbs up / thumbs down on “Did you find this page useful?” with the option to tell us more. (Early feedback I got was that a five-star system might be less desirable.)

This would be for all of our docs, but also relates to the Customer Journey efforts specific to Cloud. (See slides.)

[nrichers]

Replaced by https://github.com/elastic/qualtrics-surveys/issues/26, closing.