feat(clients): profile setting for clients

[kuhe]

This PR creates a new field, profile?: string, on AWS SDK clients. This will cause the client to function as if AWS_PROFILE were set, but limited to that client.

• needs pass client config to loadNodeConfig calls smithy-lang/smithy-typescript#1471 for completeness (max-attempts and retry-mode).
• Review the documentation change in docs(clients): document client-level profile configuration #6737
• See first commit for isolated logic changes and sample codegen for fewer clients.
  1b901b2 (#6728)