Make profile and stats API compatible with multi-category field.

[kaituo]

Description

Previously, our profile API only took one entity key and value pair in the command as parameters. Using parameters won't work when moving to multi-category fields. This PR allows users to put the entity information on the request body in JSON format.

Also, we use the GET method to call profile API. As mentioned earlier, we added a request body with entity attributes. Some CLI tools require an API with a request body that uses the POST method. So we also allow a profile API with the POST method.

What's more, we didn't show entity attributes on model output as the model id carries entity values. A multi-category entity's model id is a hash instead of concrete entity attributes. So we added the entity attributes to the response output. Similar changes are also added for stats API.

Testing done:

1. manual testing using a local cluster.

Profile API:

Sample  request:
http://localhost:9200/_opendistro/_anomaly_detection/detectors/TSB5cnkBbTSBdroveJIW/_profile/models
{
	"entity": [{
			"name": "service",
			"value": "app_6"
		},
		{
			"name": "host",
			"value": "server_1"
		}
	]
}

Response:
{
	"model": {
		"model_id": "7sF5qXkBxjkVBFJhhe5K_entity_ZoNYVJsq5ry6e-SWXmAt1Q",
		"entity": [{
				"name": "host",
				"value": "server_1"
			},
			{
				"name": "service",
				"value": "app_6"
			}
		],
		"model_size_in_bytes": 712480,
		"node_id": "LSNdy0zzR_273CGX1EFR2A"
	}
}

Stats API:

Sample request:
localhost:9200/_opendistro/_anomaly_detection/stats

response:

{
	"anomaly_detectors_index_status": "yellow",
	"anomaly_detection_state_status": "yellow",
	"detector_count": 1,
	"anomaly_detection_job_index_status": "yellow",
	"models_checkpoint_index_status": "yellow",
	"anomaly_results_index_status": "yellow",
	"historical_single_entity_detector_count": 0,
	"nodes": {
		"LSNdy0zzR_273CGX1EFR2A": {
			"ad_execute_request_count": 30,
			"models": [{
					"detector_id": "7sF5qXkBxjkVBFJhhe5K",
					"model_type": "entity",
					"model_id": "7sF5qXkBxjkVBFJhhe5K_entity_412FoQwCykWTAhjVfDGQDg",
					"entity": [{
							"name": "host",
							"value": "server_1"
						},
						{
							"name": "service",
							"value": "app_2"
						}
					]
				},
				{
					"detector_id": "7sF5qXkBxjkVBFJhhe5K",
					"model_type": "entity",
					"model_id": "7sF5qXkBxjkVBFJhhe5K_entity_FuqXh0HBXlPhKepOc6JADQ",
					"entity": [{
							"name": "host",
							"value": "server_3"
						},
						{
							"name": "service",
							"value": "app_6"
						}
					]
				}, …
				{
					"detector_id": "7sF5qXkBxjkVBFJhhe5K",
					"model_type": "entity",
					"model_id": "7sF5qXkBxjkVBFJhhe5K_entity_B4zrbSQ1-pvdBLx0FzQxvw",
					"entity": [{
							"name": "host",
							"value": "server_3"
						},
						{
							"name": "service",
							"value": "app_3"
						}
					]
				}
			],
			"ad_canceled_batch_task_count": 0,
			"ad_hc_execute_request_count": 30,
			"ad_hc_execute_failure_count": 0,
			"ad_execute_failure_count": 0,
			"ad_batch_task_failure_count": 0,
			"ad_total_batch_task_execution_count": 0,
			"ad_executing_batch_task_count": 0
		}
	}
}

Check List

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[spbjss]

nitpick: you could write as !attributes.containsKey(field)

[kaituo]

different people have different opinions about it: https://stackoverflow.com/questions/4282708/boolean-checking-in-the-if-condition

[spbjss]

Could you share some information here: why do you run search for an entity validation?

[kaituo]

Need to do it in case of typos for example. The entity is given by the API user. Not sure it actually exists or not. Added a method comment to explain.

[ylwu-amzn]

If user delete the entity after job start, then we will not be able to get this entity in index. For this case, we will not return profile for this entity even it's running on some data node?

[kaituo]

yes, the entity's model will be deleted by other entity or by maintenance due to long inactivity. Added to comments.

[spbjss]

nitpick: add * to every lines to keep the same style of the comments?

[kaituo]

added

[spbjss]

looks good to me

[ylwu-amzn]

Don't need this license header for new file

[kaituo]

removed.