Changes the configuration of the router request pipeline to move schema
validation before partitioning.
This reduces the concurrency of callsm into the schema validator when a
single write is split into one or more partitions, reducing contention
and cash thrashing. It also ensures we don't bother partitioning the
writes if the request will fail.
Adds an integration test covering the router's HTTP handler stack.
Given a well-formed HTTP write, the test asserts:
* Write passes through the stack without error
* Response code sent to client
* Write buffer message is enqueued
* Catalog namespace record is created
* Metric handler is invoked and the hit is recorded
Dom Dwyer
Marco Neumann