[Dashboard] Smoke Test Boilerplate Cleanup

[ThomThomson]

The dashboard embeddable migration smoke tests cover a lot of ground, but there are a few upgrades that can be made for speed, efficiency, and conciseness of the tests themselves.

Firstly, a draft PR for adding a testing harness will shrink our test code boilerplate significantly, but it will require some work on our side to translate it once it's merged.

Secondly, our test dashboards are currently loaded through the management UI. They will need to be translated into kbn_archiver json files, and loaded through the kibanaServer import helper.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[ThomThomson]

Closing this as the smoke tests are stable in their current form. If we need to create more, we can consider these changes and re-open this issue.