* Replace xvfb with headless browser
* Update karma to run in headless chrome
Update Karma tests for an option to run chrome in headless.
* Fix lint issues
* Fix spaces
Closes#22840
In the functional tests we want a better way to include/exclude certain tests, especially as we move forward with #22359. This PR allows us to decorate suite objects with "tags", which won't clutter up the test names and can be used to filter out specific tests within a single test config. The functional test runner supports defining `--include-tag` and `--exclude-tag` CLI arguments, and multiple can be defined.
The method of filtering out tests for running against cloud has been updated to use this approach and I plan to do the same to #22359 once this is merged.
For instances where we would otherwise be running from source in a tracked elastic/elasticsearch branch, let's use a snapshot instead. This will eliminate some gradle issues we are experiencing in master.
