Remove TagSpecification from the EC2 instance spec

[justinmir]

Description of your changes

Instance parameters allows specifying tags in two methods: TagSpecification and Tags. These methods have different semantics - TagSpecification tags will be applied when the instance is created, Tags will be created in a separate CreateTags API call afterwards. All tags required to meet IAM policy must be specified in TagSpecification.

Fixes #2024

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

This code has been tested on and deployed in our own fork used in production.

This continues to test the RunInstancesInput generation unit test that was updated to match passing in tags via the Tags field instead of TagSpecification.

[MisterMX]

I'm very reluctant about introducing breaking changes to the API. Would it be possible to keep both fields but deprecate one and have both of them being merged together?

[chris-bornmann]

If values attached to Tags are applied after creation, will this impact organizations with a set of required tags that must be present on creation? My org, and I'm certain many others, requires certain tags on instances and volumes and CreateInstance calls are blocked without those tags specified.

[justinmir]

Closing for now as I don't have the time to look at this.

I'm very reluctant about introducing breaking changes to the API. Would it be possible to keep both fields but deprecate one and have both of them being merged together?

I think this is a great solution, keeping backwards compatibility makes sense until a new version of the spec is released.

If values attached to Tags are applied after creation, will this impact organizations with a set of required tags that must be present on creation? My org, and I'm certain many others, requires certain tags on instances and volumes and CreateInstance calls are blocked without those tags specified.

This proposes using a single field that is applied when resources are created (instead of applied in a step after the fact), this still allows the same set of IAM policy that requires tags at the time resources are created. See line 825 in ec2/instance.go for the change from using TagSpecifications to Tags.

But for backwards compatibility its likely best this is changed to merge the two as an input to the RunInstancesInput.