Allow wildcard in dc when querying services

[iksaif]

It would be great to allow wildcards in https://www.consul.io/api/catalog.html#dc-1, we use prometheus to monitor services in multiple datacenters and it's pretty annoying to list all the datacenters explicitely.

[slackpad]

Hi @iksaif this would be a pretty large change under the hood - are you doing a blocking query against this endpoint or are you polling (this kind of thing would be more suitable to polling)? Can you describe how you are pulling the data in some more detail?

This is closely related to #2803 but this generalizes scatter/gather more generally than #2803 does; that one just applies it to prepared queries.

[iksaif]

I need this feature in software that are already using consul (like prometheus), I'm not doing queries by myself. It doesn't make sense to replicate this feature in every client, so I though it would be a good idea to make it possible in the API itself.

Couldn't the APIs be slightly changed to support that ? Maybe first it could be supported only by polling queries ?