Add support for billing tags

[tduffield]

Adds two new configuration values (BuildkiteBillingTagName and BuildkiteBillingTagValue) that can be used to apply a Cost Allocation Tag to instances created by the ASG.

[lox]

I wonder if these need to be configurable, vs just adding the aws:createdBy with something to indicate elastic stack.

Ideally we'd like to keep parameters to a minimum, as they make it harder for people to understand what needs configuring.

If you wanted arbitrary tags, presumably you could just use the Additional Tags section when you are creating the cloudformation stack?

[tduffield]

They need to be configurable because people may use a different tag other than aws:createdBy to manage cost centers. For example, my team uses X-Application.

As for the Additional Tags section, those are buildkite tags and we need very specific AWS tags to use in Cost Center.

Having the default be aws:createdBy should mean that most people won't need to overwrite the default. But for those who care, they can. To me that feels like a valuable parameter. Especially when it puts me in a position where I can track exactly how much $$ I'm saving using Buildkite (which is the legitimate reason why I want the tag)

[tduffield]

@lox have you had an opportunity to think on this any more?

[lox]

Yup, let's merge it in. Thanks for this and thanks for your patience, have been at AWS Summit.

[lox]

Hmmmm. The build is failing with Your account is not allowed to create tag aws:createdBy

[lox]

@tduffield I must admit, I still don't really understand why you need this if you use X-Application. You should just be able to specify that as an additional tag when creating the the Stack? For aws:* tags, I that doesn't seem to work, but should work fine for X-Application.

[tduffield]

@lox where do I specify additional AWS tags?