Code generation: Add ability for a single AWS service to use both SDK for Go v1 and v2 API clients

[ewbankkit]

Description

Currently the code generation process allows an AWS service to use either an AWS SDK for Go v1 API client or and AWS SDK for Go v2 API client. To aid with migration of large services we want to be able to support both flavors of API client in a single service.

References

Relates #27097.

[github-actions]

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[github-actions]

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