xRoute resource types contain a slice of parentRefs to services that they
manipulate traffic for. All xRoutes that have a parentRef to given Service
will be merged together to generate a ComputedRoutes resource
name-aligned with that Service.
This means that a write of an xRoute with 2 parent ref pointers will cause
at most 2 reconciles for ComputedRoutes.
If that xRoute's list of parentRefs were ever to be reduced, or otherwise
lose an item, that subsequent map event will only emit events for the current
set of refs. The removed ref will not cause the generated ComputedRoutes
related to that service to be re-reconciled to omit the influence of that xRoute.
To combat this, we will store on the ComputedRoutes resource a
BoundResources []*pbresource.Reference field with references to all
resources that were used to influence the generated output.
When the routes controller reconciles, it will use a bimapper to index this
influence, and the dependency mappers for the xRoutes will look
themselves up in that index to discover additional (former) ComputedRoutes
that need to be notified as well.
John Murret