[Draft] Migrate the CLI to v2 of the golang sdk

[wilsonge]

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Description of changes:

• Initial work on migrating the app to version 2 of the SDK (App has largely been migrated to the new SDK's with equivalent functionality). Obviously this would be a new major version of the product.

Current list of items to finish

• [ ] Some functionality has been dropped relating to the injection of regions from different sources which needs restoring (cmd/main.go)
• [ ] There's still a hard dependency on the v1 sdk endpoints package in odpricing.go which will likely require some work on the smithy side of things to generate a mapping between regions and descriptions (it's in the smithy generated json file but not in the golang sdk).
• [x] Tests are still a WIP and some more minor restructuring will likely be required as part of that.
• [ ] Propagation of contexts through the stack

Why Migrate to v2

• At the end of this the overall binary should be a bit smaller by the modular nature of the new sdk
• Some projects that depend on this (e.g. eksctl) are currently having to create two sessions - one in the v2 sdk for all their direct dependencies and one in the v1 sdk for this project
• Stronger typehints on the vm wrapper

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