Moves Instances interface methods out of aws.go

[mmerkes]

What type of PR is this? /kind cleanup

What this PR does / why we need it:

Per this PR, we need to migrate to the InstancesV2 interface. This PR does some clean up related to that migration. I moved all of methods in the Instances interface out of aws.go (and their related tests out of aws_test.go) to instances.go, which is a more appropriate home, as a first step toward eventually cleaning that code. There are no actual changes to the code. Everything was just cut and paste as is.

Which issue(s) this PR fixes: N/A

Special notes for your reviewer: This felt like a good first step in tidying up the code base and has the added benefit of reducing the size of aws.go. If reviewers disagree, I'm ok closing out this PR unmerged. I didn't move any of the underlying methods (i.e. package private methods) to keep the PR smaller and test the water on this one first.

Does this PR introduce a user-facing change?:

NONE

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[mmerkes]

/assign @cartermckinnon

[cartermckinnon]

I don't see a ton of value in moving this to a different file if the plan is to delete the code prior to 1.30, tbh. But I don't have any major objections otherwise.

Can you check if this is going to force other pending PR's to rebase?

[mmerkes]

I'll close this for now. Will sync with @cartermckinnon directly on how to best migrate/clean up this code base.