Include codegen version in releases and generated SDK metadata

[drganjoo]

Problem

Currently, identifying which codegen version is in use is difficult:

• The https://github.com/smithy-lang/smithy-rs/releases uses release dates, but the codegen version (which matches the published JAR versions) is not visible in the changelog entries.
• The generated SDK metadata only includes the commit hash, which requires additional steps to map back to a codegen version.

Proposal

1. Update the changelog: Include the codegen version number in each release entry on the GitHub releases page. This makes it easier to review what changed between specific codegen versions.
2. Emit codegen version in generated SDKs: Add the codegen version to the metadata in the generated Cargo.toml. This allows users to immediately identify which codegen version was used to generate their SDK.

Benefits

• Easier for maintainers to track versions
• Easier for customers to navigate the changelog when upgrading between codegen versions
• Provides a direct link between the published JAR version and the corresponding release