pass forwarder tags from main template

[github-anis-snoussi]

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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?