Fix command packages.

[commiterate]

Issue #, if available: N/A

Description of changes: Fix command packages.

Go by default will name commands after their package name. Switching to use this convention (also used by other AWS Go packages like amazon-ssm-agent and amazon-cloudwatch-agent).

For example, suppose the file layout is like this:

amazon-ec2-metadata-mock/
└── cmd/
    ├── ec2-metadata-mock/
    │   └── main.go
    └── ec2-metadata-mock-debug/
        └── main.go

Running go build -o build/ ./cmd/... will create this:

amazon-ec2-metadata-mock/
└── build/
    ├── ec2-metadata-mock
    └── ec2-metadata-mock-debug

Related: NixOS/nixpkgs#365690 (comment)

Please create a v1.13.0 release after this is merged.

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

[github-actions]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you want this PR to never become stale, please ask a maintainer to apply the "stalebot-ignore" label.

[commiterate]

Not stale.

[github-actions]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you want this PR to never become stale, please ask a maintainer to apply the "stalebot-ignore" label.

[commiterate]

Not stale.

[commiterate]

@Lu-David Anything else needed from me?