proposal: make DD_TAGS space separated

[alainstoffels]

We have a AWS ECS cluster which runs the Datadog agent and our services which are monitored with Datadog. We're using the DD_TAGS environment variable to set a couple of tags. We want these tags on the infrastructure hosts (which are set by the agent) and on all of our traces (which are set by this dd-trace-go package).

The agent requires these tags to be space separated but dd-trace-go requires them to be comma separated. I suggest making this consistent and thus making DD_TAGS space separated.

In our case it's quite cumbersome to pass a different DD_TAGS value to different containers within ECS so we would just like to use the same DD_TAGS variable across all our containers.

Removing comma separation would be a breaking change so it would probably be wise to keep supporting that and split both on commas and spaces

[knusbaum]

We have this in our work queue.

[katiehockman]

@knusbaum the PR for this was closed, so should we mark this proposal as rejected, or do you still feel it's worth doing?

[knusbaum]

Completed in #837