add a transform challenge

[hendrikmuhs]

add a transform challenge with 3 different transforms based on the event data track.

to be used with: --telemetry=transform-stats --challenge=transform

[ebadyano]

@hendrikmuhs Thank you for adding this! I tried running it with:
esrally --distribution-version=7.8.0 --track-path=~/rally/rally-tracks/eventdata --telemetry=transform-stats --challenge=transform --car="4gheap,basic-license" --on-error=abort

I get an error:

  ____        ____
  / __ \____ _/ / /_  __
 / /_/ / __ `/ / / / / /
/ _, _/ /_/ / / / /_/ /
/_/ |_|\__,_/_/_/\__, /
               /____/

[INFO] Preparing for race ...
[INFO] Racing on track [eventdata], challenge [transform] and car ['4gheap', 'basic-license'] with version [7.8.0].

Running delete-index                                                           [100% done]
Running create-index                                                           [100% done]
Running check-cluster-health                                                   [100% done]
Running index-append                                                           [100% done]
Running force-merge                                                            [100% done]
Running wait-until-merges-finish                                               [100% done]
Running delete-transform-group-by-terms                                        [100% done]
Running create-transform-group-by-terms                                        [100% done]
Running start-transform-group-by-terms                                         [100% done]
Running wait-for-transform-group-by-terms                                      [100% done]
Running delete-transform-group-by-geo-tile                                     [100% done]
Running create-transform-group-by-geo-tile                                     [  0% done]
[ERROR] Cannot race. Error in load generator [0]
   ("Request returned an error. Error type: transport, Description: x_content_parse_exception ({'error': {'root_cause': [{'type': 'x_content_parse_exception', 'reason': '[1:166] [data_frame_transform_pivot] failed to parse field [group_by]'}], 'type': 'x_content_parse_exception', 'reason': '[1:166] [data_frame_transform_config] failed to parse field [pivot]', 'caused_by': {'type': 'x_content_parse_exception', 'reason': '[1:166] [data_frame_transform_pivot] failed to parse field [group_by]', 'caused_by': {'type': 'illegal_argument_exception', 'reason': 'No enum constant org.elasticsearch.xpack.core.transform.transforms.pivot.SingleGroupSource.Type.GEOTILE_GRID'}}}, 'status': 400})", None)

[hendrikmuhs]

@ebadyano Thanks for pointing that out, geo tile support will be in 7.9.

Because 7.9 is not released, I can either remove the geo tile part or we wait until 7.9 is released. I think its ok to wait for 7.9.

[dliappis]

LGTM.

We'll backport to 7 branch once 7.9 is out.

[dliappis]

Backport to 7 branch in a92719a