Add support for ARM64 architecture

[ubaskota]

Issue #, if available: #1808

Description of changes:
Adds a lambda_architecture configuration option (supports x86_64 and arm64) that can be set in config.json. When set to arm64, Chalice downloads aarch64-compatible wheels during packaging, passes Architectures: ['arm64'] to the Lambda API on create/update, and emits the correct attribute in generated SAM and Terraform templates.

Usage:

{
  "lambda_architecture": "arm64"
}

Supports global, per-stage, and per-function configuration. Defaults to x86_64.

Testing:

• Added unit and functional tests to validate the changes
• Manually deployed with chalice deploy using a numpy dependency and verified the function runs correctly on Graviton. Numpy was chosen because it contains architecture-specific C extensions that will fail to load if the wrong platform's wheel is bundled.
• Generated and deployed a SAM template; confirmed Architectures: ["arm64"] is present and the function executes successfully
• Generated and deployed a Terraform template; confirmed architectures: ["arm64"] is present and the function executes successfully

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