NeonService: better integration with standard configuration

[jefflill]

Some things for the back burner:

• Evaluate integrating NeonService configuration dotnet host configuration

  I'm not entirely sure whether this makes sense, but we should at least expose our configuration values via dependency injection.

• Modify IProfileClient and the MaintainerProfile types to support querying multiple values in one go

  I believe the old op.exe CLI can handle this and this should speed things up. A good time to do this would be when we upgrade neon-assistant to use gRPC instead of named pipes and we should also upgrade to the latest 1Password CLI since we're on a very old version.

• Integrate the secret/profile value fetching into NeonService configuration code.