Migrate ECS client to aws-sdk-go-v2 in ecs-agent module

[Yiyuanzzz]

Summary

Migrate ECS client to aws-sdk-go-v2 in ecs-agent module.
#4406 added our bespoke codegen'd aws-sdk-go-v2 ECS client. This PR integrates the v2 ECS client with ecs-agent

Implementation details

In go.mod for the ecs-agent modules,

1. add a dependency ongithub.com/aws/aws-sdk-go-v2/service/ecs
2. add a replace directive so that we use our bespoke ECS package instead of the official SDK package

replace github.com/aws/aws-sdk-go-v2/service/ecs => ../aws-sdk-go-v2/service/ecs

Update ECS client construction per the docs.

Replace all uses of our v1 ECS client with the v2 ECS client.

• Package aws/aws-sdk-go/service/ecs is now split between aws/aws-sdk-go-v2/service/ecs and aws/aws-sdk-go-v2/service/ecs/types.
• Many pointer types are now non-pointers (e.g. ContainerStateChange.NetworkBindings changed from []*NetworkBinding to []NetworkBinding). See the docs for more info.
• Many int64 types are now int32 (e.g. NetworkBinding.ContainerPort and NetworkBinding.HostPort changed from *int64 to *int32).
• Many string constants now have their own enum types aliased to string (e.g. the AgentUpdateStatus* constants changed from string to type AgentUpdateStatus.
• ErrCode*Exception string constants have been replaced with Exception types (e.g. ErrCodeAccessDeniedException ("AccessDeniedException") now corresponds to the AccessDeniedException type).

Testing

GitHub checks pass.

New tests cover the changes:

Description for the changelog

Migrate ECS client to aws-sdk-go-v2 in ecs-agent module.

Additional Information

Does this PR include breaking model changes? If so, Have you added transformation functions?

Does this PR include the addition of new environment variables in the README?

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.