R1:c85327ca3e58

Give AlmanacServices a service type

Summary:
Ref T5833. This allows services to be typed, to distinguish between different kinds of services. This makes a few things easier:

- It's easier for clients to select the services they're interested in (see note in T5873 about Phacility). This isn't a full-power solution, but gets is some of the way there.
- It's easier to set appropriate permissions around when modifications to the Phabricator cluster are allowed. These service nodes need to be demarcated…