Adopt go modules

[r4v5]

Adopt Go modules for dependencies, removing the existing /ecs-cli/vendor directory and replacing it with a best-effort-possible recreation of what it contained.

Note that dep ensure on current mainline actually generated a bunch of changes that resulted in non-compiling code, so a lot of the commit-based module references are best-effort guesses from what I saw in the vendor dir.

This successfully passes go test when run in an ubuntu 22.04 devcontainer, and the code generation (including the license.go vendor dir auto-creation) still works. I don't have a Windows machine handy to test the functionality of the resulting application, but it's working under Linux and Mac aarch64.

I also created a devcontainer configuration for folks who don't have a Go 1.13 binary hanging around.

The initial intention here was to upgrade the aws-sdk-go version in order to use ARM64 in Fargate and enable container execution (which I have working on a separate branch, though the code doesn't compile under Windows). As a result, I ended up unwinding some of the dependency situation here and figured it'd be useful for other people.

Fixes #994.

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Testing

• Unit tests passed
• Integration tests passed
• [N/A] Unit tests added for new functionality
• Listed manual checks and their outputs in the comments (example)
• Link to issue or PR for the integration tests:

Documentation

• Contacted our doc writer
• Updated our README

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