cloudwatch_event_target: Add ecs_target

[kjmkznr]

Add ecs_target parameter to aws_cloudwatch_event_target resource.

This feature can set run task based on CloudWatch Event Trigger.

$ make testacc TEST=./aws TESTARGS='-run=TestAccAWSCloudWatchEventTarget_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSCloudWatchEventTarget_ -timeout 120m
=== RUN   TestAccAWSCloudWatchEventTarget_basic
--- PASS: TestAccAWSCloudWatchEventTarget_basic (36.85s)
=== RUN   TestAccAWSCloudWatchEventTarget_missingTargetId
--- PASS: TestAccAWSCloudWatchEventTarget_missingTargetId (20.25s)
=== RUN   TestAccAWSCloudWatchEventTarget_full
--- PASS: TestAccAWSCloudWatchEventTarget_full (98.58s)
=== RUN   TestAccAWSCloudWatchEventTarget_ssmDocument
--- PASS: TestAccAWSCloudWatchEventTarget_ssmDocument (29.25s)
=== RUN   TestAccAWSCloudWatchEventTarget_ecs
--- PASS: TestAccAWSCloudWatchEventTarget_ecs (31.22s)
PASS
ok      github.com/terraform-providers/terraform-provider-aws/aws       216.171s

[stack72]

This LGTM! thanks for this @kjmkznr

% make testacc TEST=./aws TESTARGS='-run=TestAccAWSCloudWatchEventTarget_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSCloudWatchEventTarget_ -timeout 120m
=== RUN   TestAccAWSCloudWatchEventTarget_basic
--- PASS: TestAccAWSCloudWatchEventTarget_basic (52.68s)
=== RUN   TestAccAWSCloudWatchEventTarget_missingTargetId
--- PASS: TestAccAWSCloudWatchEventTarget_missingTargetId (31.73s)
=== RUN   TestAccAWSCloudWatchEventTarget_full
--- PASS: TestAccAWSCloudWatchEventTarget_full (99.30s)
=== RUN   TestAccAWSCloudWatchEventTarget_ssmDocument
--- PASS: TestAccAWSCloudWatchEventTarget_ssmDocument (34.07s)
=== RUN   TestAccAWSCloudWatchEventTarget_ecs
--- PASS: TestAccAWSCloudWatchEventTarget_ecs (30.50s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	248.313s

[ghost]

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