pass forwarder tags from main template

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What does this PR do?

Add the ability to set tags for the forwarder lambda from the main cloudformation template.

Motivation

Having multiple AWS accounts with DataDog integration requires manually setting DD_TAGS to env:my_env in the Forwarder lambda in the AWS Console, otherwise logs will have env:none .

Another niche reason is having to manage the integration with CDK ( example code bellow ), and with each deployed update to the integration, I have to set the DD_TAGS in the integration again.

new cfn.CfnStack(this, 'datadogIntegration', {
  templateUrl: 'https://datadog-cloudformation-template.s3.amazonaws.com/aws/main.yaml',
  parameters: {
    ExternalId: externalId,
    DdApiKeySecretArn: apiKey.secretArn,
    DdSite: 'datadoghq.eu',
    CloudTrails: cloudTrailBucket,
    LogArchives: logArchives,
  },
});

Testing Guidelines

This is how I manually used to achieve having environment tags in the forwarder lambda.

Additional Notes

Anything else we should know when reviewing?

DataDog / cloudformation-template