feat: Publish releases on Swift Package Registry

[jbelkins]

Issue #

awslabs/aws-sdk-swift#1553

Description of changes

• Change smithy-swift back to being distributed via Git
• Added a version property to service clients so they are aware of their own version & can report it in the user agent
• Removed parameterization on package manifest name. There is a new Gradle property in the aws-sdk-swift PR for controlling whether package manifests are copied for service clients.
• A few other minor fixes

Scope

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

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