Query Service: Combine SSE handling in single tenant and multi tenant paths (#108041)

* parse via sse

I need to figure out how to handle the pipeline.execute with our own
client. I think this is important for MT reasons, just like using our
own cache (via legacy) is important.

parsing is done though!

* WIP nonsense

* horrible code but i think it works

* Add support for sql expressions config settings

* Cleanup:
- remove spew from nodes.go
- uncomment out plugin context and use in single tenant flow
- make code more readable and add comments

* Cleanup:
- create separate file for mt ds client builder
- ensure error handling is the same for both expressions and regular queries
- other cleanup

* not working but good thoughts

* WIP, vector not working for non sse

* super hacky but i think vectors work now

* delete delete delete

* Comments for future ref

* break out query handling and start test

* add prom debugger

* clean up: remove comments and commented out bits

* fix query_test

* add prom debugger

* create table-driven tests with testsdata files

* Fix test

* Add test

* go mod??

* idk

* Remove comment

* go enterprise issue maybe

* Fix codeowners

* Delete

* Remove test data

* Clean up

* logger

* Remove go changes hopefully

* idk go man

* sad

* idk i ran go mod tidy and this is what it wants

* Fix readme, with much help from adam

* some linting and testing errors

* lint

* fix lint

* fix lint register.go

* another lint

* address lint in test

* fix dead code and linters for query_test

* Go mod?

* Struggling with go mod

* Fix test

* Fix another test

* Revert headers change

* Its difficult to test this in OSS as it depends on functionality defined in enterprise, let's bring these tests back in some form in enterprise

* Fix codeowners

---------

Co-authored-by: Adam Simpson <adam@adamsimpson.net>

pkg/expr/dataplane_test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/grafana/grafana/pkg/services/datasources"
 	datafakes "github.com/grafana/grafana/pkg/services/datasources/fakes"
 	"github.com/grafana/grafana/pkg/services/featuremgmt"
+	"github.com/grafana/grafana/pkg/services/mtdsclient"
 	"github.com/grafana/grafana/pkg/services/pluginsintegration/pluginconfig"
 	"github.com/grafana/grafana/pkg/services/pluginsintegration/plugincontext"
 	"github.com/grafana/grafana/pkg/services/pluginsintegration/pluginstore"
@@ -70,6 +71,7 @@ func framesPassThroughService(t *testing.T, frames data.Frames) (data.Frames, er
 			Features: features,
 			Tracer:   tracing.InitializeTracerForTest(),
 		},
+		mtDatasourceClientBuilder: mtdsclient.NewNullMTDatasourceClientBuilder(),
 	}
 	queries := []Query{{
 		RefID: "A",