Implement per-route options in route-emitter

[maxmoehl]

Proposed Change

In RFC0027 Generic Per-Route Features we decided to implement a new field for routes which can contain additional, custom configuration for a route. Together with this new feature we also want to implement the first property making use of it: customisable load balancing algorithms.

This new field must be implemented in route-emitter to announce this field via nats to gorouter. This depends on support in BBS which is tracked in #939. If possible, route-emitter should not consider the contents of the per-route options. It can expect that the content is JSON encoded and can be emitted as part of the message as-is.

Acceptance criteria

• route-emitter emits the new field via nats.

Related links

• RFC tracking issue: [RFC0027] Generic Per-Route Features community#909