added functionality for custom tags from DD_TAGS environment variable

[aldegoeij]

in order to pass tags like "prod", or "environment:prod" to all cloudwatch messages processed by the lambda, I've implemented similar functionality as for the DD docker container.
Using the DD_TAGS environment variable, which you can set in your CloudFormation or Terraform (like we do), as additional metadata["ddtags"].
Also minor whitespace on the '+'s.

[NBParis]

Hello @aldegoeij .

First of all, thanks a lot for your help on making Datadog a better product.
The idea to collect tags from an environment variable is indeed very interesting and we would be pleased to add it.

Would it however be possible to add a check in your PR to make sure we do not try to add it to the list of tags if the environment variable is empty?

Thanks a lot,
Nils

[dmulter]

I was about to submit a PR, and saw this was already submitted. Looks to me like it already handles the case where the env var DD_TAGS isn't set. Can we see this merged sometime soon?

[NBParis]

Hello @dmulter,

Indeed, sorry for forgetting about this one.
And it indeed handles it correctly in case it is not set (misread the code on my first review...)

We will do some tests and merge right after.

[NBParis]

Works perfectly.