CBD-4857: Update screenshots to 7.1.0

[udkyo]

This change is quite noisy because I've re-run the generator. The important part is what's happening in the generate directory:

• Updated the readme template to reference images as url/foo.jpg, rather than url/version/foo.jpg - so we can update the images in place without a pull request to docker-library/docs going forward
• Changed the css text being targeted from setup-sample-beer-sample to bucketbeer-sample so that the field can be selected correctly - the name has changed since 6.6.2 when the screenshot generator was last run
• Updated the compose file to drop the version number from the output folder - the idea being we'll just overwrite images in the root of the target bucket to update them in future

[ceejatec]

@mhocouchbase No, changing these files by themselves won't trigger any builds that I'm aware of.