Add ecs-agent/ ACS model + cleanup gogenerate make

[danehlim]

Summary

Create ecs-agent/ directory, and add ACS model and gogenerate to that directory.

Update/clean up existing gogenerate make targets in Makefile.
Prior to this change:

• make gogenerate does not actually run go generate at all
• make gogenerate-init runs go generate for both agent/ and ecs-init/ directories

Implementation details

1. Add ACS model and gogenerate to ecs-agent/
   • Copy agent/acs/model and agent/gogenerate to ecs-agent/acs/model and ecs-agent/gogenerate
   • Go into ecs-agent directory and run go mod init and go mod tidy
   • Modify versions in ecs-agent/go.mod to match those in agent/go.mod
   • Run go mod tidy and go mod vendor
   • Generate new ACS JSON model file per ECS Agent standard operation procedure that is in sync with up to date source of truth provided by control plane, and then replace agent/acs/model/api/api-2.json and ecs-agent/acs/model/api/api-2.jsonwith the newly generated file
   • Run make get-deps and make gogenerate (dependent on below implementation detail). This replaces agent/acs/model/ecsacs/api.go and ecs-agent/acs/model/ecsacs/api.go with newly generated files
2. Clean up gogenerate make targets
   • Update make gogenerate-init target to run go generate only for ecs-init/ directory
   • Update make gogenerate target to actually run go generate, and run it for agent/ and ecs-agent/ directories

Testing

Unit, integration, and functional tests.
Manually test modified make targets locally with make command.

Description for the changelog

Add ecs-agent/ ACS model + cleanup gogenerate make

Licensing

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