Ability to tag resources (Event Types, Functions, and Subscriptions) with metadata

[alexdebrie]

When registering Event Types, Functions, or Subscriptions, a user may want to tag them with particular metadata, such as the service it belongs to. This is comparable to Kubernetes labels -- metadata that is meaningful to the user but not to Event Gateway itself.

Example implementation:

{
    "functionId": "createUser",
    "type": "awslambda",
    "provider":{
      "arn": "arn:aws:lambda:us-east-1:377024778620:function:users-service-dev-createUser",
      "region": "us-east-1"
    },
    "metadata": {
        "service": "users-service"
    }
}

For now, this would allow for client-side filtering of resources based on metadata.