Consider including permissions version on non-UI poolsStreaming api response

An excerpt from an #ns_server discussion between Dave Finlay & myself on realizing updates to local users during Cheshire-Cat:

For local users we do have something: there’s a version hash on the checkPermissionsURI in the pools/default payload for the UI, but not for non-UI pools/default requests. You could fake this, but I’d probably prefer you didn’t. Of course the UI uses it for similar reasons - it tosses its permission cache if it changes. It’s a little on the heavy side to compute in terms of how it leans on the configuration, but it might be ok to add to the general pools/default response, we’d need to think about it. It’s computed based on users version, user groups versions and authorization parameter versions (collections and buckets).
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For local users, I think you could use the versioning on the checkPermissionURI that I described above and it should work OK for your use case.

It would be quite helpful to have this in a streaming API, to avoid repeated permissions fetches on local users by analytics.

As for timing, we could take advantage of this as early as 7.0.1, otherwise 7.1 would be helpful as well.