`on_premises_instance_tag_filter`
When setting `on_premises_instance_tag_filter`, Terraform was not
pushing the changes on the cReate (due to a spelling mistake). A second
apply would push the tags and then cause a panic. Terraform was building
a ec2.Tagfilter struct without checking for optional values. When the
TagFilter was being dereferenced, it caused a panic
* Improve testing of CodeDeploy DeploymentGroup Trigger Configs
- ensure updates to trigger_events are applied
- assert changes to trigger_target_arn
* Retry CodeDeploy DeploymentGroup when Trigger Config SNS Topic is not available
- increase retries from 2 => 5
* provider/aws: CodeDeploy Deployment Group Triggers
- Create a Trigger to Send Notifications for AWS CodeDeploy Events
- Update aws_codedeploy_deployment_group docs
* Refactor validateTriggerEvent function and test
- also rename TestAccAWSCodeDeployDeploymentGroup_triggerConfiguration test
* Enhance existing Deployment Group integration tests
- by using built in resource attribute helpers
- these can get quite verbose and repetitive, so passing the resource to a function might be better
- can't use these (yet) to assert trigger configuration state
* Unit tests for conversions between aws TriggerConfig and terraform resource schema
- buildTriggerConfigs
- triggerConfigsToMap
