Tests: Adds end-to-end tests skeleton and basic smoke test scenario (#16901)

* Chore: Adds neccessary packages

* Wip: Initial dummy test in place

* Feature: Downloads Chromium if needed

* Fix: Adds global config object

* Refactor: Adds basic e2eScenario

* Build: Adds end to end tests to config

* Build: Changes end to end job

* Build: Adds browsers to image

* Build: Adds failing test

* Refactor: Adds first e2e-test scenario

* Fix: Ignores test output in gitignore

* Refactor: Adds compare screenshots ability

* Refactor: Removes unnecessary code

* Build: Removes jest-puppeteer

* Fix: Replaces test snapshots

* Refactor: Creates output dir if missing

* Refactor: Changes aria-labels to be more consistent

* Docs: Adds section about end to end tests

* Fix: Fixes snapshots

* Docs: Adds information about ENV variables

public/app/plugins/datasource/testdata/partials/query.editor.html

@@ -3,7 +3,7 @@
 		<div class="gf-form">
 			<label class="gf-form-label query-keyword width-7">Scenario</label>
 			<div class="gf-form-select-wrapper width-15">
-				<select class="gf-form-input" ng-model="ctrl.target.scenarioId" ng-options="v.id as v.name for v in ctrl.scenarioList" ng-change="ctrl.scenarioChanged()"></select>
+				<select class="gf-form-input" ng-model="ctrl.target.scenarioId" ng-options="v.id as v.name for v in ctrl.scenarioList" ng-change="ctrl.scenarioChanged()" aria-label="Scenario Select"></select>
 			</div>
 		</div>
 		<div class="gf-form gf-form gf-form--grow" ng-if="ctrl.scenario.stringInput">