Expose route manifests to other services via api

[devinmatte]

Motivation

So we don't have to copy the manifest files or lists of routes/stops in multiple repos, expose what the dashboard currently supports via API

Changes

• Creates two new API endpoints, one that exposes supported routes, and one that exposes supported stops for a route
• Enables doing more complex data ingestion jobs for buses and other routes where there's more than just the few rapid transit we currently support

Testing Instructions