Add Session Header for Query Tracking/Routing

[whitleykeith]

This issue is to ask for some session-level headers that can be used for routing within service-mesh enabled environments to enable zero downtime deploys. If there's other options that anyone knows about, I'm open to discuss :)

We currently use Trino daily to support large, complex data workflows. Some of our queries can take hours to complete, and it's widely used across different timezones, meaning we don't get a lot of low traffic time to deploy changes to our Trino cluster, which has become a bottleneck for us.

We have Trino installed in a K8s environment on top of a service mesh. Currently when we update our Trino cluster, all of our running queries are killed, which can cause our workloads to fall behind. We want to be able to deploy a new revision of our Trino cluster, route new queries to it, and continue routing existing sessions to the old Trino cluster. We need both of these revisions to serve the same host.

If we had some session level header that we could set on the initial response to the POST of a new query that would get passed to subsequent calls to nextUri we could set that to the revision of the Trino cluster and be able to effectively drain queries from the old revision before promoting.