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>

.github/CODEOWNERS

@@ -150,6 +150,7 @@
 /pkg/services/hooks/ @grafana/grafana-backend-group
 /pkg/services/kmsproviders/ @grafana/grafana-operator-experience-squad
 /pkg/services/licensing/ @grafana/grafana-operator-experience-squad
+/pkg/services/mtdsclient/ @grafana/grafana-datasources-core-services
 /pkg/services/navtree/ @grafana/grafana-backend-group
 /pkg/services/notifications/ @grafana/grafana-backend-group
 /pkg/services/org/ @grafana/grafana-backend-group
@@ -178,7 +179,6 @@
 /pkg/setting/ @grafana/grafana-backend-services-squad
 /pkg/tests/ @grafana/grafana-backend-services-squad
 /pkg/tests/apis/ @grafana/grafana-app-platform-squad
-/pkg/tests/apis/query @grafana/grafana-datasources-core-services
 /pkg/tests/apis/alerting @grafana/grafana-app-platform-squad @grafana/alerting-backend
 /pkg/tests/api/correlations/ @grafana/datapro
 /pkg/tsdb/grafanads/ @grafana/grafana-backend-group