Add support for Graviton2 powered Lambdas

[matthias-pichler]

Expected Behavior

Since lambdas now support both the x86_64 and arm64 architectures there now exist two different lambda layers for the extension: Datadog-Extension and Datadog-Extension-ARM

The macro should read the architecture of the lambda function and add the correct layer

Actual Behavior

Only the x86_64 layer is suported

Steps to Reproduce the Problem

1. create a cloudformation stack with a lambda runnin on Graviton2
2. configure extensionLayerVersion: 11
3. deploy
4. invoke lambda

Specifications

For the Datadog Serverless Macro:

• Deployment method and version (CloudFormation, SAM, CDK): CDK
• Datadog CloudFormation Macro version: 0.2.1
• Lambda function runtime (Python 3.7, Node 10, etc.): Node 14

[hghotra]

Thanks @matthias-pichler-warrify! I merged your PR.