WIP: Spawn backend plugins v2 (#19835)

* WIP: Spawn backend plugins v2

* Add test for plugin version

* Fix support for SDK plugins

Co-authored-by: Kyle Brandt <kyle@kbrandt.com>
Co-authored-by: Marcus Olsson <olsson.e.marcus@gmail.com>
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

* WIP: Draft PR for fork of V2 sdk / bi-directional support (#19890)

* temporary use export-datasource-plugin branch of grafana-plugin-sdk

* fix failing test

* remove debug (spew) lines

* misc cleanup

* add expressions feature toggle

* use latest grafana-plugin-sdk-go

vendor/github.com/google/flatbuffers/go/lib.go

@@ -0,0 +1,13 @@
+package flatbuffers
+
+// FlatBuffer is the interface that represents a flatbuffer.
+type FlatBuffer interface {
+	Table() Table
+	Init(buf []byte, i UOffsetT)
+}
+
+// GetRootAs is a generic helper to initialize a FlatBuffer with the provided buffer bytes and its data offset.
+func GetRootAs(buf []byte, offset UOffsetT, fb FlatBuffer) {
+	n := GetUOffsetT(buf[offset:])
+	fb.Init(buf, n+offset)
+}