add new annotation (header-value)
parse it and propogate to lua script
alter balancer rule to include it into the canary routing logic
add e2e test to validate fallback for canary-by-header-value
add description of canary-by-header-value to documentation
Adds the ability to create alternative backends. Alternative backends enable
traffic shaping by sharing a single location but routing to different
backends depending on the TrafficShapingPolicy defined by AlternativeBackends.
When the list of upstreams and servers are retrieved, we then call
mergeAlternativeBackends which iterates through the paths of every ingress
and checks if the backend supporting the path is a AlternativeBackend. If
so, we then iterate through the map of servers and find the real backend
that the AlternativeBackend should fall under. Once found, the
AlternativeBackend is embedded in the list of VirtualBackends for the real
backend.
If no matching real backend for a AlternativeBackend is found, then the
AlternativeBackend is deleted as it cannot be backed by any server.
