Prevent duplicate service tags

Hi,

I have a situation where I'm using nomad job templates provided by a service with custom tags. I've created a wrapper to be able to specify additional tags during deployment. Problem with that is that Consul allows duplicate tags (which makes sense as I expect tags are an array). This leads to pollution of service tags.

Wouldn't it be better to use a `set` instead of an `array`?

Btw, for now I'm just going to check member existence in my wrapper to prevent this but IMHO it would be nice if Consul already did that.