Add assorted environment fixes for search development

[csutter]

Note: I've only just started working on search and it is entirely possible that some of the things I've changed are intentional and I'm misunderstanding some parts (and this could break people's workflows). Please be extra vigilant and don't assume I must know what I'm doing! 🐛

This is a set of changes I have had to make to get to a point where I can reliably publish a document in whitehall and get it to show up in finder-frontend. Several apps either intentionally or accidentally weren't able to talk to their service dependencies, or refused to build or start.

• Add missing RabbitMQ configuration to publishing-api-app and publishing-api-worker
  • This is causing publishing-api-worker to be unable to listen to the message queue, leading to errors and missing data
• Configure router-app to not require VCS information at build time using GOFLAGS
  • In some (possibly non-deterministic for me) circumstances, router-app refuses to build with a Go error: "error obtaining VCS status: exit status 128", which this works around
• Add missing ROUTER_NODES environment variable to router-api-app
  • This is causing router-api-app to be unable to talk to router-app running as part of GOV.UK Docker (it tries to find it on localhost), causing errors when upstream applications try to add new routes
• Add RabbitMQ configuration to main search-api-app
  • The lack of config (it's set in the x-search-api anchor template but overwritten by the search-api-app configuration) is causing some setup tasks to fail as the app cannot talk to RabbitMQ
• Add dependency on whitehall-worker to whitehall-app
  • This currently isn't a dependency, so it isn't starting the worker when starting the app, leading to background tasks never running